They did do that, every agency exists with a mandate.
SCOTUS just decided that despite the madnates existing, being funded, and being regularly renewed, that's not good enough.
But they haven't defined how specific the mandate and laws must be. They can just, you know, keep shifting the goal posts until they get the desired result.
Thats all people here want. Whatever power it is that you think that agencies should have, try to pass a law to do that first.