Why should China uphold maritime law when US doesn’t?

First of all, in his response yesterday to this story, Facebook user Dan RK Sparkman did not answer my question as to why China should uphold the rule of law in the disputed South China Sea when the US doesn’t? Please answer. 
Second, the arbitration “court” in The Hague cannot give a binding verdict but is merely an advisory stage to be taken into account when a real court case is started.
In my opinion, the Vietnamese are following America’s wishes in Southeast Asia, and the Philippines have broken loose from this. All the wrangling in this region is instigated by a world power losing clout and desperate to regain past influence. 
Andre Machielsen