The only reason some people are still making a lot of money selling cannabis is because the state law on medical marijuana has never been fully implemented, and local governments severely limit the number of suppliers.
When cannabis is truly legalized, the price will drop to a point at which no one is going to make a killing from selling it. This might be bad for tax revenues, but it would good for everyone else.
Whether you approve of marijuana use or not, and whether you believe it has medicinal uses or not, selling marijuana is one of the few growth areas in our economy. Still, we refuse to tap into this potentially huge tax revenue resource.