Sometimes the men with guns are also distributed across multiple continents, and the only way to protect yourself from them entails making a deal with
other men with guns.
If you’re part of a multi signature scheme and you’re hiding from US authorities in, I dunno, China or Russia or Pakistan or Afghanistan or Iran, there’s (a) not much stopping Uncle Sam’s boys from sneaking up on you anyway if they’re sufficiently motivated and (b) some local men with guns whom you might need to deal with as well.
In reality it’s probably not worth it for the US to track you down to the ends of the earth and/or get the CIA involved if you’re just trying to sneak some ill-gotten money out of the country, and it’s a lot easier for one of your multi-signature holders not to get caught than for the authorities to simultaneously catch up with a quorum. And maybe your group includes some people who really don’t mind living the rest of their lives in these types of places.
But for those of you who live within the greater American empire, the price you pay for keeping that money out of Uncle Sam’s hands is going to include keeping it out of your hands and also you go to prison if you ever get caught. Which is probably a bad deal unless you’re a drug cartel or some other group that’s already sort of priced in that outcome.