Inmates engaged in such schemes and plans are kept busy and functioning in a civil manner in order to not draw attention or focus on their behavior. If they are taking drugs of the right type, their behavior is subdued even more.
The supply chains need to be torn down every time power bases begin to form on distribution rights. Then the whole thing starts all over again. It's a cat-n-mouse game, with the cats and mice quite docile as long as they are playing the game.
Meth, cocaine, and amphetamines of other types must be kept out with no exceptions. Those are too problematic.
My dad worked in a prison. We followed the story of a group of lifers who were docile pussycats as long as they kept their still operation going on the prison farm property. They would move it each week. Every few months it would get discovered, smashed up and inmates would get punished in some way. The new one would be up and running again in another month. During that month the farm inmates were busy as little worker bees, so they behaved like saints.