They may be starting to lose steam as a business. Take a look at these numbers for one private prison corporation for example.
Personally I'm on the fence about private prisons, but regardless I felt this was worth mentioning.
Private prisons are no more free market than the post office or utilities. Free enterprise is not about companies, it's about consumer choice. I don't care about this issue any more than any other governmental issue. It has zero to do with capitalism either way