He does not have the authority to make it apply to the States.
It's in Article 6
This Constitution, and the Laws of the United States which shall be made in Pursuance thereof; and all Treaties made, or which shall be made, under the Authority of the United States, shall be the supreme Law of the Land;
...and the
Single Convention Treaty on Narcotics that the US instigated and signed, is what cause weed to be Constitutionally illegal.
You may not like it, I may not like it, but the Constitution says what it say. Not what we might like it to say.
I agree, but the way to do it is by having "leaders" that want it to work that way. As long as virtually everyone going to DC see's the Constitution as a hinderance to be creatively overcome, we'll never get that.