Because the current criminal "justice" system has very little to do with actually preventing and helping society recover from the effects of criminal behavior. It's about generating false appearances of "retribution" (or making people "pay" for their crimes, whatever that means), and the (deeply) false appearance of some kind of "moral balance" in the world, generally. And reinforcing systems of (low-key) terror and control on the general population.

It only encourages people to revert to evil.

You got it. That may not be the stated goal of the current system. But it's certainly one of its inevitable outcomes.

The tragedy is that it's not just the offenders - or even those wrongly accused - who suffer from (and become morally corrupted by) the current order. It's all of us.