I think it's worth thinking about the history of incarceration, for context. Until fairly recently, prison wasn't really the way most punishments worked. They did hangings, beatings, shaming, banishment... Imprisoning people long term is expensive, and kings probably couldn't have afforded anything like a modern scale prison system. The closest thing was more slavery than imprisonment, and economically self-sufficien…
Are you suggesting we've actually TRIED rehabilitation? If so, I think our definitions differ. We haven't tried anything besides incarceration.
Other places have rehabilitation, and it appears to work.