Why not? It would be another source of money for capitalist companies who can make a buck off it. I would be surprised if there were not several large tobacco companies who would give up the evil weed for the good weed entirely.
Why not indeed. It's just that some people are skittish about commercialization. And there are some precedents: In some European countries, wine production is heavily regulated and taxed, except at wine taverns on a vinyard property. Pot commerce could be kept similarly low key. Besides which, being a Federalist, I would allow states and localities to continue to make selling pot illegal.
I am sure some people though the end of Prohibition would be the end of the world, too.