I'm glad you asked. I work for a non-profit called Ameelio (ameelio.org) that is working on that. We started with free incoming (to the facility) mail (aka letters) and expanded to free video and voice calling, and are currently working on expanding further though I don't want to say exactly what at this point.

To answer your question though, yes entrenched interests and lack of competition. When you are sole provider, no matter how broke people's families are they are going to dig deep. Some states also allow a "kickback" system where the department gets a % of the fees collected by the providers. Fortunately some states have made this illegal and more are starting to now that we've shown how corrupt and gross the incumbent situation is, but there's still a way to go. I will also say that I've been impressed with a lot of people in the departments. Many of them don't like the current system either and they think it's wrong, so they've been really helpful/willing to work with us.

Related past thread: https://news.ycombinator.com/item?id=23042558