This Frontline doc (2013) paints a nice picture.

https://www.pbs.org/wgbh/frontline/film/retirement-gamble/

Many pension funds are screwing their members with high fee mutual funds resulting in 2-3%+ haircuts on annual returns. And this does not include all the mystery fees on top of everything else. Imagine what the compounding effects on this is. And these funds are shitty compared to Vanguard index fund over time. It comes down to shady backroom deals, kickbacks and incentive based selling.

edit: added year of the doc.