Why is homebrewing so middle-class, straight, white, male?

You need enough money for the gear, but also be a beer person.
- Not so much the first part. Home brewing is one of the easiest low cost for entry hobby.

You're conflating correlation with causation.
Causation: Most homebrewing is a moderately expensive hobby, and so will skew toward middle class people
Correlation: where you are located, middle class people are probably majority white. Also probably the majority of people in your area in general are white. Also the majority of people in general are straight.
If you were in Japan or Colombia or Jamaica, middle class people would not be majority white.
As for the male thing, brewing beer is viewed as a more masculine hobby. Call it a self fulfilling prophecy. Many women probably choose not to join the hobby because they view it as not something women should do.
As an aside, it's helpful to learn about Bayesian statistics in order to interpret trends and observations that you see in the world around you. Here's an example:
Paige is a young woman. Paige enjoys reading books and has a quiet demeanor. She also enjoys drinking coffee and watching romantic comedies.
What is more likely?
A) Paige is a ~~teacher~~ librarian
B) Paige is a farmer
Most people answer ~~teacher~~ librarian, but the answer is that Paige is overwhelmingly more likely to be a farmer. Simply because there are orders of magnitude more farmers than ~~teachers~~ librarians in the world.
Edit: this would have made more sense if I said librarian instead of teacher. Let's all just pretend I did 😅
- Most people answer teacher, but the answer is that Paige is overwhelmingly more likely to be a farmer. Simply because there are orders of magnitude more farmers than teachers in the world.
  But are there more farmers named Paige or teachers named Paige?
  I can’t imagine Paige is a common name in many of the countries which still rely on subsistence farming, where farming will be a far more prevalent occupation. In the US, where Paige is a relatively common name, there are around twice as many teachers as farmers according to my very brief (and probably not super accurate) research.
  Also I imagine that worldwide, farmers will skew male more than female. Just like how teachers probably skew more female than male. Note I didn’t bother to look for statistics for this, this is just a guess.
  If you were to not name a person or gender and just say “is this person more likely to be a teacher or farmer,” then sure, farmer. But we’ve limited our base group of people to women named Paige. Surely that adjusts the probability.
  
  Even if her gender and name adjusts the probability somewhat, it should all still be cancelled out by the order of magnitude by which the number of farmers outnumbers teachers, even in countries where a name like Paige is common. Teachers are an incredibly uncommon profession in the grand scheme of things, because it only takes a small proportion of them for a society to function (no offense intended to teachers of course)
  But I will admit, I believe the original version of this thought experiment didn't give the woman a name. I was just trying to be a bit more descriptive haha. I'm pretty sure the thought experiment also predates the level of automation that is now common in agriculture. I was mostly just reconstructing it from memory.
  Edit: yeah I just looked it up and in the US there is roughly the same number of teachers and farmers (around 3.5-4 million). I guess this particular version of the thought experiment is dead. But you could construct a similar one with a more common profession. Or just pretend it's still the 60s when you give your answer. Farming has simply become way too automated in the modern era.
  Edit 2: I'm just now realizing the original version of this that I heard was with librarians, not teachers! Librarians are actually still orders of magnitude less common than farmers so it would work in that case. This is what I get for relying on memory for my clever comments.

Hey, I think I can be an outside voice here, while I am white, I'm poor, queer, and learned homebrewing from my Hispanic father in law making tepache.
Given my experience with the Mexican brewing community and the rural white folk brewers in my area, I think the barrier here is just internet use. My father in law speaks limited English so he's kind of adverse to forum conservation. The stillers back in my home town didn't need the internet, they learned it from their parents and talked about it with their neighbors.
For my part, I came here to bridge the gap and make something a little more white, middle-class, straight. My fil's tepatche is a dinghy grey paint water, mine is a crisp, clear amber. I don't see any dandelion or mulberry wine here, but champagne yeast makes for a better taste then bread yeast.
If you're looking for something different, pick a random fruit and see how we've used it for alcohol, because we've absolutely used it for alcohol.

I hope that one day we can judge people not by the color of their skin, but by the quality of their brew.

Because all the cool people are too busy homebrewing tabletop RPGs instead.

The middle class part makes sense. You have to be someone who both owns their own property and also has significant leisure time.
- As someone who makes meads/wines in a closet and has done so while renting, I don't particularly see the relevance as long as your batches are small and contained... Typically, the tools and ingredients aren't wildly expensive either if you're keeping things simple (in the US, anyways). Honestly, I don't see how more demographics don't get into the basics of homebrewing. It's dead simple to make something "passable" and with time and effort you can even make something good/great!

I thought this was about modding Wii and DS systems… oof
- I just assumed. Homebrewing seems to rarely refer to actual brewing.
- lol, there is a lot of confusion when I'm researching things or buying parts.
  
  "Why would I need a soddering gun to make beer???"

Mostly because it's seen as hipster and mostly straight white dudes were the most enthusiastic adopters of the hipster aesthetic.
Plus a lot of different cultures have different cultural traditions related to preferred drink and drinking practices, not all of which lend themselves easily, or even safely, to homebrewing.

I am a lady and I ferment plenty of stuff, both drinks and foods. But don't like beer, so I don't make it. The only guy I know who makes beer is a white guy, so my experience mirrors yours, but it's also true that there are minority run commercial breweries and distilleries so I'm sure there is home brewing going on too.

Got better things to do, don't drink alcohol or too poor to waste time like that but I don't know about middle-class white women.

You aren't wrong. For me, I wanted cheap imperial stout all year long. It's hard to find, and it's always expensive, and happens to be my favorite. And I fit your demographic.
Maybe as a whole, DIY is a "middle class white" thing. Crafting, home improvement, gardening, etc. and beer is just a male-centric version of that.

That's probably the same demographic that praises craft beer from brewery businesses, so I think the question should be taken back a step from DIYer to consumer. Here's my interpretation from the US, matching the demo in question.
I'd guess from an economic status, lower income doesn't have the money to spend on craft beer and higher income would transition towards wines. Even though wine and beer can both be made in less than 2 months, beer typically doesn't benefit from aging but wine typically does - meaning better wines incur higher overhead costs for storage for better wines.
From an ethnic standpoint, I don't think I can pin it on anything other than being the majority demographic of the English-speaking world (with your survey/groups possibly being US/Canada focused). Beer is certainly a global phenomenon, but keep in mind your sources will be based by language. However, Germany is the only country I can think of outside of North America where I'd expect diverse craft beer. Maybe their surrounding countries and England too. Everyone makes alcohol, but they may put more resources into wines and spirits instead. Ethnicity likely also ties into financial status on a global scale so once you account for language bias, you'll lose countries that don't have the national spending available for such craft beers.
As for gender, I would put that down as a mix of beer being seen as manly - large quantity of liquid, not sweet, makes burps. Sweet and brightly-colored drinks make many men worried other men might think they're gay (gods forbid you enjoy a tasty drink). So that gives straight men drinking beer and everyone else mixing it up.
Where does that leave us? Straight white middle class men drink craft beer, which spills over into the homebrew English-speaking community demographic.

As someone not American. Is it something that you do frequently wherever you go or do? Construing statistics about the people around you? And then being displeased about some fluke in the numbers? Like what does it matter?? I genuinely dont understand.
- Construing statistics about the people around you?
  Huh? I don't understand the question.
  And then being displeased about some fluke in the numbers?
  Where did I say I was pleased or displeased?
  Like what does it matter??
  Look at the name of the community you're participating in.
  
  What I mean about constructing statistics is going to a place and starting counting people hmmm yes there are 95% straight people here and 96% white people here …. Like do you really do that?
  
  You are right this is no stupid questions and im sorry if I came out a bit judgmental or rude. That was not my intention.
  I just dont really understand why it matters and why people put so much emphasis about the (racial? Gender? Class?) composition of people in “X”. I just cant fathom going to a place and think boy I wish there were more X here. Is it an American thing?

Too bad lemmy doesn’t have a “prisonhooch” community as far as I know. That tends to attract far more people as it costs less

Why does the wind blow? Why do the tides rise and fall?
- Because you touch yourself at night, Jimmy!
- And magnets? How do they work?
  You can't explain that!
- Look at the name of the community. Your response isn't really helpful.

Back ten, twenty years ago you basically had to go to Europe to try good beer. Who was traveling to middle class white Americans.
Starting a brewery before recently was often a mark that someone had time and info to practice brewing at home, interest in European food and history, plus the start up capital/safety net to start the business.
Now a bunch of relatively privileged people who think it's possible for them too....

Probably because middle class straight white men are often very exclusionary.