You can thank the Fed. Pensions and their consultants publish an assumed rate of return, which is increasingly difficult to obtain in a sustained low interest rate environment. They have been increasing exposure to private markets to compensate for low returns in fixed income("yield seeking"). There is additional pressure since public and private pensions are typically underfunded, and overly aggressive return assumptions give cover to the states and companies that don't fund them to the extent they should.

Like many things the answer is extremely simple.

Because they are not the ones paying the cost of mismanagement, and they have a captive audience that is both legally prohibited to go elsewhere, and practically ignorant of how mich they are getting screwed.