The reason is that resentencing people is a low priority when the justice system is falling apart in so many other ways. The authorities also don't want to be

The reason is that resentencing people is a low priority when the justice system is falling apart in so many other ways. The authorities also don't want to be held to account for traumatising these people and any crimes they subsequently commit. 12 years is a murder tier stint, so pretty much all of them should just be released. However releasing a lot of dangerous people looks bad even if it's morally justified.