Poor users seem to enjoy a lot of legal alcohol. Taxes on that are high too, and it's even easier to make your own alcohol than to make your own weed.
It sure as fuck isn't. There are parts of the world where putting some free seeds in the ground is sufficient.
It's pretty hard to mess up growing weed bad enough to hurt someone, unless you poison yourself with pesticides on accident (which aren't really necessary at least at the personal scale). If something bad happens, it's almost always to the plant.
Selling flower buds of a plant will hardly be accessible. But the industry will eventually find a way to make a viable cannabis product from waste.
But it's an awful lot easier for a dealer to sell weed to a hundred people than for them to sell bottles of alcohol to a hundred people.
Individuals can and do make their own alcohol -- and it's a really expensive hobby to get it right. In terms of price per unit volume, distribution of illicit alcohol is quite problematic. You can easily fit $500 of weed into 1 liter (local prices and densities vary). Retail booze is less than a tenth of that. Bad booze would be even lower. This is a substantial impediment to the risk/reward calculus for street-level sellers all the way up to producers.