reading the whitepaper , it seems everything will be managed by the swiss company. facebook is just one of the partners.

[As another user mentioned, the company that makes the wallet is US based and will enforce sanctions. But maybe that means that another of the partners can make a wallet to use in sanctioned countries?]

If it's based in Switzerland why would US law apply to it?

Because as some have found out, US law kinda applies everywhere.

https://en.wikipedia.org/wiki/Raoul_Weil

The better question is "Why does Facebook think that being based in Switzerland will protect them?

It's been a while since Swiss banks were last immune to U.S. government pressure. Or even pressure from other countries. I can't bother to find the links now, but there were a couple of stories during Obama's time, about the US government arresting people based on their financial transactions in Switzerland.

Because the US can go after every single American company that's part of the association that runs it.