I believe almost international banks require SSN for US citizens. It’s a US thing and why Swiss banks are less popular. US IRS doesn’t want its citizens to hide money in other countries and pressures foreign countries to comply
Heh, then I guess you do not know the lengths the IRS goes to track the income of US persons wherever they are. Double taxation of US citizens has even pushed some dual citizens to renounce their US citizenship...
The IRS requires that local banks take the personal data of US citizens simply because it does not trust Americans to cooperate willingly. And I think that's a fair assessment, because no one would willingly pay taxes to two countries at once.
If you're required to pay taxes in the US for any reason, you have to give just about any bank in the world that will accept you either an IRS form W9 (citizen or "US person") or W8-BEN (anyone else).
That's because of FACTA. I know some banks over here (France/Western Europe) outright refuse US clients because they don't want to deal with that stuff.