Private prisons are only part of the revenue generated from the war on drugs. Civil forfeiture is a huge income stream for local and federal. They basically wait for the drug dealers to sell their drugs and then catch them with the money and take it. Some police departments allot for 35% or more of their annual budget to come from civil forfeiture. Add to that the amount of federal money received to fight the war. Also fines and fees. There is a lot of money changing hands and jobs being created by prohibition.

It's not just private prisons, it's the correctional officer unions too. They benefit greatly from large prison populations.

That can be a very misleading number.

8.4% owned, how many are not privately owned have services/goods/staff provided in large part by private companies?

There's always someone who makes this comment, and I'll say the same thing I said before: https://news.ycombinator.com/item?id=8562814

Which is still greater than the ideal of 0%.