I do not think it is quite as simple as that. Pension funds often invest in bonds because they provide reliable cash flow, but for the past 30 years bond yield

I do not think it is quite as simple as that. Pension funds often invest in bonds because they provide reliable cash flow, but for the past 30 years bond yields have been falling, to the point where 3% on a 10-year treasury is considered big news today (it was much lower just a year ago). For the past 10 years interest rates have been kept artificially low as part of the response to the great recession, but pension funds have still had to make their payments. Retirees are also living longer thanks to advances in healthcare. It would not have been easy to predict those longer lifespans decades ago when they were first promised their pensions, but the pension still has to keep paying as long as they live. None of this is to say that governments have no share in the blame for this. Failing to take action to stabilize these funds, or worse, cutting taxes when the money could have been used to help keep the funds solvent, was a bad decision too many states made.