Because the multiple trillions of dollars we've already spent trying to instill common sense into people, the multitude of social programs designed to try and help people get jobs or a roof over their head, the grants or subsidies to help people start their own businesses and all the other programs who in one way or another have tried to set people on the correct path to life have worked so well we should spend trillions more.
The easiest way to reduce the prison population and those committing repeat crimes is to execute people. Domestic violence. Gone. You don't beat the crap out the woman (or man) you're living with and think that's acceptable.
You don't have multiple crimes against you before you're 18 then get a free pass to start the process over. Rapes, child molestation/rape, recidivists, murderers in general, gone.
Clean out the system instead of coddling and you will see a dramatic improvement in society. With the criminals gone, who will commit the crimes?