It's essentially that once you leave prison you have zero resources, usually all your friends are gone, often your family shuns you, you can't get a job due to

It's essentially that once you leave prison you have zero resources, usually all your friends are gone, often your family shuns you, you can't get a job due to your record and lack of skills, you can't rent any accommodation due to background checks, and you are on a knife-edge parole that will send you back for any tiny infraction. And it's easy for someone to just give in and go back to prison. Prison is only scary the first time. After that you walk back in and meet people you know who don't judge you. You know the staff. You know the routines. Do a few more years for the parole violation and see if things have changed next time around. If not, repeat ad infinitum.