But Prohibition ended quickly after it began. There is a long history of illegal drug trafficking in the US. The infrastructure is all there.
The only way to eliminate the illegal drug traffic is to undercut the illegal dealers and the exact opposite is happening. The legal weed is much more expensive. The beauty is that the government can’t tell if the weed you are smoking is legal or not.
You can always depend on the government to find a way to screw up a perfectly good solution to a problem.