There is a third primary reason, and it is one that artbrooks dismisses - the refusal by voters to pay sufficient taxes to pay for the enormous cost of civilised prisons needed for such enormous numbers of prisoners, numbers which arise because of the existing criminal system and cultural/economic structure of American society.

There's a political corollary of "if you can't do the time don't do the crime". It's "if you can't pay the cost, don't buy the policy".