Cutting off their testicles and straight up executing them would also reduce the offending rates. Even more effectively than chemical castration, I’m sure. But we wouldn’t be calling that helping the offender, would we? And the comment above was specifically talking about helping them.
What we have now is more of a best middle ground between the amount of damage caused to the patient and safety guarantees for the society. We obviously prioritize safety for the society, but we should be striving for less damage to the patient, too.