One thing that has always amused me as a German is that for every banking/investing account I have ever opened they always included one question: Do you have an USA citizenship?
I assume with online banking this has become less of an issue, but apparently having US clients as a non-US bank is a massive hassle that no one wants to touch.
It's still a thing. The US thinks it's hot shit, wants banks all over the world to comply with extra requirements for US citizens, which no other country does. Banks don't want to deal with it. Ordinarily they'd just ignore stupid requirements coming from stupid countries like China, but when it's the US they don't want to be sanctioned.
Thankfully, the US is now trying to delete its special position so we may soon be in the situation where stupid requests from the US are treated the same as stupid requests from Russia.