I mean it's all encrypted, right? Most cloud providers even allow you to specify your own encryption keys. Sure, the NRO isn't going to start uploading all their sat imagery to a gcp bucket, but I'd imagine it's fine for everything that's not classified.
Heck, even for the classified stuff, I heard Azure built a government owned datacenter running a self hosted copy of their software. Much better quality than asking some Gen Dynamics contractor to manage everything for you.
They don't though. Swiss tax wealth (though its a tiny fraction). IRS makes it a massive PITA to hold substantial financial stakes in foreign companies. See FATCA and GILTI. And many tax deferred foreign retirement funds are not treated as being tax deferred by the IRS. It only gets more complicated from here. It's by far easier to earn and hold cash in America.
That was many years ago. The entire Western world is compromised and reports to the IRS -or- the bank kicks out anybody who MIGHT be a US Citizen to avoid being sanctioned. The end result is only the few most central banks in the country take American clients -or- they are hopelessly behind on regulatory compliance (YOLO).