Much better immediate punishments could be devised if the goal was deterrence, but society has phased those out. The modern philosophical justification of prison is physical separation from society and environment to prevent repeat offenses.

Making prison "suck less" might even give inmates a shot at a life after they are released. But given that you see prison "suckage" as a feature (especially given the generally accepted ideas of what goes on in prison), I can only conclude that you've ruled out any possibility of yourself ever ending up there, and thus don't really care.