im not sure if they do this in the states or not, but here in canda while you are in jail/prison (anything 6 months less a day is just reagular jail) you are forced to take classes (ex. wood working) so you are better suited to succeed in the community upon your release.
Ive been around this stuff my entire life, my dad is a criminal defense lawyer her in Windsor and i can say first hand that people do change. Ive seen countless people fuck their lives up by commiting a crime and once they are sentenced and released they are a completely different person. Are there people who reoffend? of course, but in certain situations living in jail and/or prison is better then not living in jail for some of these people. While in jail they are given food, shower, bed, heat, which for most criminals is more than they have in their real life so they will reoffend (sometimes more seriously than before) to get all of those things back.