The chess game is more complicated than the editors discuss.
If China were to stop oil shipments to DPRK the Kim regime would collapse quickly. DPRK's missiles can easily reach all major Chinese cities. All players understand these 2 points.
Upon taking power, Kim immediately realized his country's dependence on China and has determined the surest way to ensure his survival is the nuclear threat - against China. Kim has not dared visit China since taking power. He knows he would certainly be apprehended, & China & its collaborators inside the regime would seize control of DPRK. The shock 2013 execution of Kim's uncle Jang Song Thaek & others, was required to reduce China's influence inside the regime, send a message to any would-be traitors, & tell China Kim will not be a puppet.
A decisive economic move by China to force DPRK to stop producing nuclear tipped missiles will easily be portrayed by DPRK as a betrayal of their friendship. In a nuclear exchange, China has far more to lose.