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...

Then IRS should have information about foreign accounts. And guess what, they already ask for that. It's fine.

The other way around is what I find concerning.

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.

When I was in China, they accepted my US passport number for things like opening bank accounts. Things may have changed, but I doubt it.

You have to do that in pretty much any foreign country because of FATCA — assuming they’ll allow you to open a bank account at all.

No banks ask me for my SSN in Thailand when I open accounts. They report as required by FATCA. Presumably your US passport number is adequate.

To add more specifics to the other comments:

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).

The US government requires this.

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.

They probably already have it anyways. From the extensive apt campaigns.