The purposes of criminal justice include (this list is based on the Sentencing Act 1991 in Victoria):
- Rehabilitation of offenders
- Denunciation ('this behaviour is wrong')
(Retribution can also be a purpose.)
What the question is talking about is rehabilitation. As discussed in the book 'Starship Troopers', you can't expect a person to improve their behaviour if they are not shown how. Some simple examples in practice include violent offenders being sent to anger management classes, or bad drivers being sentenced to remedial training.
Why aren't all offenders put into rehabilitation programs? Some reasons include:
- Cost. It would be very expensive to offer all the rehabilitation which would help all offenders.
- Often this kind of thing is court-ordered, so if the judge does not know about relevant programs or does not assess the offender's needs correctly, then the offender will not be sent to them.
- The offender is unwilling to participate in programs that are available, and there are limits to how much coercion a given society is comfortable applying.
There is no 'one size fits all' rehabilitation. Some people need to talk about what makes them use drugs, others need to talk through their childhood issues, others need training so they can get a job and not fall back into bad habits when they are released from prison. Perhaps North Korea has a great curriculum for putting lots of people in a camp and they come out model citizens, but I'm not aware of the details.
Can a person really be forced to do anything? Even the army can't do that. The army might put you in prison, but that's redundant for a person who is already a prisoner. You can always threaten to kill them, I suppose, whip them, or brainwash them with electrodes perhaps, but that depends on your principles as a society.
I think it's fair to say that, these days, the trend is towards what the question suggests, which is putting as many offenders as possible into rehabilitation. In 2014 it was reported that Texas took the money it would have spent on building a new prison and used it on rehabilitation instead, and there were suggestions that that worked well.