I've grown a lot of pot over the years. Its ridiculously easy. And you just use it as a herb if you want the easiest way to take it in or buy a vaporizer.
It's easy to grow plants. Growing them for optimal output, fungus free, testing, processing, and assuring quality product is more than just keeping them warm, proper sun, and watered.
And I haven't even touched on the social aspect yet, even under legalization, people are still very scared and judgemental of MJ.
Most of your production and sales will be at a store front and run by businesses, that's just how it is. Some people will grow for personal use, it's just not gonna be prevalent enough to worry about taxing them.