I think what a lot of people are missing in this thread is that not everyone has access to convenient physical stores and many people do have good reasons to want faster shipping.
For example, young families who don't live near a Walmart. When you realize you need a few things for the kid, it can be pretty tough to pack them up and drive however far to the store that may or may not have what you need. If they do have it, you aren't going to get reviews or many options.
My recent prime purchases have included bottle brushes, a crib mattress protector, a replacement remote for our sound bar (dog ate it), and a cheap car camera to check the baby since he started daycare last week and I'm completely paranoid about my ADHD brain leaving him in a hot car and killing him.
Did any of these need to be prime purchases? I guess not but you can see how I would want them sooner rather than later.
Walmart near me didn't have any good car cameras in my price range.
The sound bar remote was online only and was required for us to watch TV since our TV speaker doesn't work.
The bottle brushes were just convenient.
The mattress protector could have waited but would have been a gamble on ruining our very expensive crib mattress. This could have been a a Walmart purchase for sure though.
I'm not saying these were life or death purchases. They weren't and people got by just fine before Amazon. But does the convenience and reliability outweigh the monthly prime cost? For us, yes. And I admit we have become pretty dependent on it.