Prison is not designed to be a place for rehabilitation. Prison is designed as:
A profit center
A method for people who want to exert control over the populace to do that
It is, as you said, actively hostile to the goal of rehabilitation. Some of that is deliberate, because recidivism is further profit for the people involved in the system, and some is just how it happens.
The system also happens to occasionally fulfill a useful goal of keeping violent or dangerous people off the streets, but almost every single other thing that it does is harmful.
Prison is not designed to be a place for rehabilitation. Prison is designed as:
It is, as you said, actively hostile to the goal of rehabilitation. Some of that is deliberate, because recidivism is further profit for the people involved in the system, and some is just how it happens.
The system also happens to occasionally fulfill a useful goal of keeping violent or dangerous people off the streets, but almost every single other thing that it does is harmful.