Problem is, prisons like all government institutions are controlled by fads and fears and money - Senators don't do anything until votes are at stake or campaigning dollars. So nothing happens for a long time, and then Bang some extreme measure is passed to show that they care or something.

We closed the mental institutions and released folks into the general population, and that didn't work very well. Closing the prisons would be worse, because some of the people in there actually mean to do us harm.