LED grow lights have dramatically reduced the cost and effort required to set up a grow and allow you to alter the light composition easily, to trigger the various phases of growth.
And it’ still not free. You still have to drop a fair amount of money at the beginning. And you have to have the space. And then you are STUCK and have to take care and watch the plant. No more long vacations for you!
Growing is fine and dandy if you can swing it, but only a small amount of people ever will.
Brewing beer is even LESS of a hassle and yet most people aren’t going to go through the effort for much of the same reasons. The time and money just sin’t worth it for the large majority of people.
And greenhouses? I live in a tiny ass apartment, where the fuck am I and most people going to put a greenhouse? And who is going to pay for the materials? And who is going to do the building?
Growing marijuana is not the same as growing a freakin’ tomato.