I'm not an expert by any stretch, but my understanding is that plenty of pensions have steep early retirement/termination penalties, especially in state and municipal service. And if the full pension benefit was already small, any penalty may reduce it to an unlivable level.

As an anecdote, a relative -- who had 25 years of public service when he was 57 years of age -- would have only received 35% of his pension if he had taken early retirement (or jumped ship to private industry) at that time.

Keep in mind, also, that most public employees are ineligible for Social Security. And most of these economically distressed towns tend to be concentrated in counties and states with severe debt issues, where raiding pension funds is not uncommon. And sadly, benefit reduction continues to be an option in public debt discussions.