He doesn’t because he doesn’t want to send a bunch of Mexican young adults who grew up in the US and while illegal, never had ties to Mexico. He can’t give them citizenship so they are stuck in limbo until a law can be passed. The optics are horrible if he does send them back and Trump is really not that mean of a guy. It needs a legislative fix and Trump has many battles on his plate!
But he already attempted to rescind DACA. Are you suggesting he did so in bad faith, knowing it would fail in court?