You don't need to put "US" there, government/corporation overreach is a thing in every country.

Most countries couldn't care less about imaginary US property. The US forces them to care via trade agreements.

Most countries start to care very quickly after the US calls them and discuss matters.

Any centralization is fragile. Github is more fragile than what is possible, but there is little point on improving that.

Indeed, but they DO care about THEIR imaginary property, and because of that they usually don't need to be forced to enter those trade agreements as you seem to believe.

Git is decentralized. You can download a repo from anyone else who has it provided they expose those files to the internet.

Obviously. But that doesn't mean that you know where those other people are without some central place to communicate that, say a 'git hub'. There is a reason Github was served with these DMCA notices: it's a very effective choke point.