I don't mean the prison(er) labor. Prisons employee not just guards but doctors and nurses and groundskeepers and secretaries, plumbers, electricians, HR, food service companies... Just like colleges or military bases, prisons are a source of jobs for the surrounding area and can be the only thing keeping them even vaguely economically viable.

Making the slave labor illegal wouldn't get rid of most of the economic/political incentive for prisons.