If BuyMeACoffee is actually just trying to comply with sanctions, that still applies even if they're facilitating payments via cryptocurrency. If the reason why they're sticking to just Stripe really is in part fraud prevention, well, I... Do I really need to comment more? I badly wish cryptocurrency was the savior for a deeply broken ecosystem of payment processors but it simply isn't, it's not easy to use, it's very easy to lose money, transactions can be slow and expensive. It could be/could have been great for the sadly growing segment of payments involving legal, consensual transactions between parties that are pushed away by traditional payment processors, but so far it isn't/hasn't been and I don't think it will be. Maybe some day.
(I do realize you are specifically speaking of stablecoins but as far as I know they struggle from all of the typical problems you'd expect, just with a less volatile value.)