they doubled down on previous assertions that issuing or brokering tokens for crypto triggers money transmission (AML/KYC) law. after the SEC made this very explicit, we saw lots more ICOs prohibiting investment from the USA.
well most of them aren't even in US to want to comply with US laws. they come from Asian countries. and as you mentioned many of them even reject US citizens so asking for KYC becomes even shadier! besides we have already seen lots of KYC related documents that people submitted for the ICOs have been sold on the dark market.