Brother, with that much stash of bitcoin, the US can make powerful economic moves that can alter the decentralization of the network. This is only in theory as we are yet to have a full-on scale attack to alter decentralization so far. It is not new that US will want to lay claims to the network and might resort to other means to do it.

It's similar to how there are downsides if a major player accumulate so many Bitcoins. Only this time, it's the US government at play.