Strange, Big Tech has no inherit right to operate in foreign markets. If they want to be in those markets, they need to pay their fair share. I would be glad to see them pull out of those markets, but that won’t easily happen.
Think of it on the flipside. If I make a website, I don't control who accesses it, and if I run ads or something, figuring out where that revenue is coming from is quite difficult. It can be done, but if I have to pay taxes to a hundred different countries, that's quite the burden.
I don't know how DSTs work in practice, but ideally we'd just discourage ads in general. Paying taxes on actual transactions (sub fees and whatnot) is easy, and ads suck.
These taxes usually have minimum revenue requirements that smaller players wouldn't meet. Canada's DST requires at least $20m in Canadian digital services revenue and €750m in global revenue.
It's actually pretty easy to know which country an IP belongs to. ARIN, RIPE, etc all keep public databases tracking what ASN blocks are allocated to each country.
And then you need to go file tax forms in each of those counties, track which ads were seen by which IP block, etc. If you're a smallish company, that's a nightmare, esp. if it's relatively small numbers for each country.
Something like sales tax/VAT is easy since you can probably have your payment processor handle it, but if you're monetizing through ads/affiliate links, you're in for a world of pain. That's awful, and I honestly would just block huge swaths of the would instead of dealing with it until my business got big enough.
If you want competition against big tech, this isn't how you do it.