Should have worn a suit.
The US is not an ally of Ukraine, it sees Ukraine as a nuisance that should have rolled over long ago but somehow refuses to and because the US still needs Europe for a bit longer (but maybe not that much longer) they're still playing ball as long as Europe pays (as it should, but that's besides the point).
Allies come to each others aid, the US has all but abandoned Ukraine after Trump came to power and did far less than it could have done early on. Why you would expect Ukraine to be generous after the numerous put downs and actions that were clearly organized to benefit Putin is a mystery to me.