There's a big difference in brewing your own beer and tobacco It costs money to do both. Wanna grow your own tobacco? You're going to have to have the land to plant it, good soil, the correct season, the time, and the hard work of picking it, planting it, plowing it, then drying it out and everything else that goes along with preparing it either for smoking, dipping, or chewing.
As far as alcohol goes you're going to need all of that and more and it's simply not worth doing unless you are some kind of moon shiner or just really want to drink you're own alcohol.
Which is exactly what you said, i'm just using those points to contrast.
Weed is much different. It's easier to manage and grow and it's simple to pick. There's no processing, fermenting, and much less know how required to do it. If weed was legal 80% of the users would simply grow their own weed or buy it under market value from one of their friends that had a surplus.
Again, not saying anything is wrong with weed other than it being illegal. I'm only saying it being legalized does not mean that people will stop growing it/selling it. Surely not on the same scale as they do now.. but it will not be like tobacco nor beer in the same sense.
Growing weed is not as easy as you make it out to be. Maybie growing shitty weed which no one would buy. But do grow even decent weed it is much harder and costs a lot more then you make it out to be.