If we cared about this, then why is revenge the core focus on American justice system and not rehabilitation? When people exit the prison system un-rehabilitat

If we cared about this, then why is revenge the core focus on American justice system and not rehabilitation? When people exit the prison system un-rehabilitated they will hurt more people. I think this is a more important question. Why is revenge given priority over avoiding new victims? Also if one actually cares about life, why are prisons such overcrowded hell holes that prisoners get shanked and killed on a regular basis? This is my issue with this sort of reasoning as it easily becomes cherry picking of issues to support harsher justice system while ignoring all the related issues which speaks for a milder system.