because their justice system isn't about revenge
Well, exactly! Where's the money in that?
Seriously though, you have the issue dead-to-rights here. If we want rehabilitation, there are known methods we could employ to make a considerable improvement to the recidivism statistics. Other countries have achieved results worth looking into.
That suggests revenge is of much more importance to society than an actual resolution to the problem.
We're taught that people who do 'bad things' are 'bad people'. There are precious few of us who develop into adults capable of questioning this. In time a little introspection can resolve this blurry question into a clear focus on the real issue: 'why do people do bad things?' Another angle suggests that 'people are not their behaviours'.
People behave the way they do through learned behaviour. Violent people are enacting learned behaviours that they perceive grant them a little short-term power for a medium-to-long-term loss that doesn't matter because it's not happening right now. Persistent short-term thinking is a hallmark of a being in 'survival mode'. They'll never prosper in this state, nor will they interact well with others.
We must see this for the inherently-correctable behavioural issue that it is, because the consequences otherwise are a steadily-inflating prison population and an ever-widening gap between the attitudes of the average citizen, the police enforcing the law and the judiciary meting out an acceptable form of justice.
