I have a theory. 

China doesnt want the US in Asia. They don't want a one Korea controlled by the south as SK is friendly to the US. Japan is as well, that is enough, China wants the East to be the The East, not the West rubbing shoulders. Russia would off course be happy with keeping the US out. I feel this is nothing to do with PRNK, they are a very very handy pawn. The three of them might want the US to go a bit far military wise. Could happen under Trump, who many feel was helped into power by Russia. Its just a power game between Russia and China vs the US. I'm sure China looks as themselves becoming the dominant power economically, sooner than later. They get on well with Europe. All of this leaving the US out in the cold.

All the news and hype about PRNK actually has very very little to do with them, in my opinion. I also see Russia and NATO are having their own military exercises near the Russian border. Russia also probably has aims for more then Crimea.