For-profit prisons are a horrible idea, especially given that they lobby for harsher sentences and for more crimes to have mandatory minimum sentences. Private prison companies have spent many millions of dollars through lobbying and campaign donations as this article from the Washington Post in 2015 outlines.

https://www.washingtonpost.com/posteverything/wp/2015/04/28/how-for-profit-prisons-have-become-the-biggest-lobby-no-one-is-talking-about/?utm_term=.49a09a9ef687

They aren't spending millions without an expectation of very lucrative returns on the investment.