>foreign banks that ask you whether you're a US citizen

Note that this is largely the case for any bank where you're not a native to their country - because of the Common Reporting Standard. However the US asymmetrically applies FATCA instead of the CRS.

https://en.wikipedia.org/wiki/Common_Reporting_Standard#Mult...

"The U.S. receives information relating to US citizens' accounts from many countries due to the compliance requirements of the FATCA. The United States, in many cases, will reciprocate by sharing banking data with countries for accounts which their citizens hold in the U.S., but not automatically, as is required by the U.S. in FATCA."

This makes serving US citizens in an "average" financial institution an added burden that might not be considered worth the cost.