North Korea is a tool of China.
To ‘resolve’ North Korea involves engagement with China, and China will use their tool to manipulate the US wherever and whenever possible.
China really doesn’t care about the Norks per se, but it is a tool to try to bring the South Koreans into the fold, as part of their new “Greater East Asian Co-Prosperity Sphere”.
It’s ridiculous to think the Chinese really want the Norks controlling the whole peninsula.
Also, South Korea and China don’t want millions of Nork refugees coming over their borders, as would happen if the situation there destabilized.