I think the problem might be marijuana's autonomy and capacity as a "stand-alone, self-propelling" substance. tobacco is still pretty difficult to grow and process, but weed, well.... they call it weed for that reason- itll grow anywhere. Legalize it, and tons of ex-tobacco smokers will seen converting to homegrown weed.
Then again, i don't even know..... how difficult is it to grow and process your own tobacco, anyway? I know some of the wives tales about home grown weed are true, but tobacco? anyone ever done it?