What is "the prison"? A state run organization? In that case why would some bureaucrat care if his budget goes up, he's a union member most likely thus his pay is more related to time employed than the budget being fiscally sound. Now consider this is a private prison, why would they ever not release someone? Releasing someone lowers their costs and may provide a reward, on the other hand they have to continue to pay for a prisoners upkeep and have no chance at a reward if they vote for him to stay.

This is all moot because it isn't prisons that decide who gets to go free but a parole board. That's part of a judicial process typically unaffiliated from the prison itself.