China is not afraid of U.S.
Historically China is a quasi enemy of Russia.
Russia was plotting to nuke China in 1969 over their border conflict. They have rarely liked eachother and are not traditional allies.
https://en.wikipedia.org/wiki/Sino-Soviet_border_conflict
https://www.scmp.com/article/714064/nixon-intervention-saved...
https://www.bloombergquint.com/global-economics/chinese-stat...
It’s almost explicitly Western policy at this point that Russia would be better a Chinese vassal than regional power. If Putin winds up dependent on Beijing, that isn’t great, but it’s better than the current situation.