> I believe the enforcement is federal (ATF).
It is not. The Feds, if they legalized could put federal enforcement there, or somewhere else.
In California, enforcement is in the Department of Cannabis Control.
> ATF also has some pretty sweeping powers that may be tough to replicate (legally) on a state by state basis.
Because the federal government is mote Constitutionally restrained than state governments and has a Constitution that is more difficult to change, its much easier to create state agencies with sweeping powers (within the state) than federal ones.