We have normalized the treatment of the financial and payments systems as things that exist primarily to perform law enforcement surveillance functions. It's the same dynamic that leads to debanking of small accounts - payments firms exist on thin margins and the potential fines for inadvertently servicing a bad actor are stratospheric, so it's entirely logical to play it safe by refusing to service anyone whose profile looks even the slightest bit risky.
These companies aren't public utilities, no one would complain about a US bank not doing money exchange business with entities in the Ukraine or Belarus, why would that be different for US companies offering donations over the Internet? The fact is that all platforms that facilitate cross-border money transfers between two parties without clear services or good being exchanged are used for all kinds of money laundering, and governments try to contain that for good reasons. In the end they probably don't care much about the revenue they make in these countries as it's probably negligible. Again, their good right to do so, I don't see any issue with this at all.
What's wrong with a US bank sending money to Ukraine? Sure, they might ask for an explanation, but I doubt they will reject. Example: You need to send money to a family member (immediate or extended), or want to donate directly to the national treasury (yes, you can do this), or another war-related non-profit. These are all legit. There is probably more risk in money transfers to Bulgaria or Romania, due to online scammers. Belarus is a wholly different matter. They are one step away from Russia-level sanctions, due to aiding Russia during the invasion of Ukraine.