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.
The occupied parts of Ukraine are under sanctions and presumably banks are concerned they can't differentiate the precise destination in country. Safer to just blanket deny everything.
> What's wrong with [...] You need to send money to a family member (immediate or extended),
I tend to agree, but the same applies if one family member is in Belarus or Russia, and the other one is in the USA.
I.e. just because it's morally ok, it doesn't mean that it's without risk (if you lie about the purpose) and that the banks will facilitate it.
OTOH, before EO2022, I know that transfers between Russia and countries in Europe were sometimes still happening. Disappointintly (but it's not very surprising), sending small money to family would usually be impossible, but if you had to transfer substantial amounts of money, and you could prove that it was from e.g. sale of a home, that could still happen.
On one hand, that makes sense: the bigger the amount, the more it makes economic sense to allow extra time and effort to check that all the i are dotted and all the t ate crossed.
But OTOH, the people with lots of housing property are sometimes precisely using housing to launder the provenance, and they are also not necessarily the honest workers whose family end up split across borders.