It’s kind of a viscous cycle. Politicians have convinced themselves, and lots of voters, that private industry is cheaper than “government run.” They forget that the only time that might be true when there’s sufficient competition in the market to drive costs down - which there usually isn’t. They also forget that private companies’ motive is profit, not rehabilitation. In fact, rehabilitation is the last thing they want. You’ll find that private correctional companies often lobby pretty hard for stricter laws, and tougher sentencing guidelines. Now, why do you think these companies would want MORE people in prisons!?