What good would it do if China hacks Bitcoin? Bitcoin doesn't belong to any country.

If you mean being able to hack Bitcoin by the use of 51% attacks, which is pretty much the only attack that they can execute, then you're wrong. In terms of the global transaction volume, Bitcoin isn't used by any government as a store of value. It would make sense if you could paralyse another country by restricting their financial flow but it can't be the case. The most that they can do is to stop the citizen from using Bitcoin which doesn't really affect people since most of the transactions are in fiat as of now.