DACA status is temporary under the DHS regulation. Like a driver's license, it has to be renewed. The lower court said it was within the executive's power to not grant any new DACA immunities from certain immigration laws; but he had to accept renewal applications.
At bottom, the argument was similar to "reliance."
It's a BS argument from the court, because it, itself, stomps all over reliance when it feels like it. The general rule is anything the government can give, the government can rescind (except DACA).
So he “has to” keep accepting applications. Doesn’t have to approve any!