Launch codes aren’t to block China from authorizing a launch. They’re there to keep someone in the military from doing a launch without authorization. China is probably one of the parties who least wants said codes leaking.
If you have a couple hundred people who can start a nuclear war, that war becomes a whole lot more likely than if only one can.
From China’s standpoint, the next best number of people who can launch against them after 0 is 1.
The British used bicycle keys on their nuclear bombs.