The Soviet Union was a Unitedstatesian enemy. China is a political and economic competitor but not an enemy. At least not now or for the foreseeable future, you don't lend a trillion bucks to your enemies.
Nixon and Kissinger successfuly tied China to the US economy.
China's prosperity depends on the US and EU markets.
China wouldn't do anything to harm the goose that lays the golden eggs even if the eggs are periodically devalued.