Indeed. While I think this is a problem (see my comment on the Cash for Kids atrocity), I've never ever seen any sign it's a big problem, as in there being all that many private prisons. Between the political power issues noted by others that push for government prisons, and people's instinctive realization that this is dangerous, I see this at worst being a self-limiting problem. Especially after the first scandal like the Cash for Kids atrocity surfaces with Republican politicians to blame.