Interesting paper making this point by Curtis & Ayres.
A lot can go wrong in 401k plans. Investors can make bad choices and fail to diversify. But, the plan provider can also cause problems by giving investors a menu with lots of high fee options. Apparently this is common.
My University took us out of TIAA-CREF a couple years ago and sold us to Fidelity, who were only going to offer actively managed relatively high-fee funds. Faculty complained and some index funds and some TIAA-CREF grandfathering were allowed. But we constantly get bombarded with emails from Fidelity.
Anyway, Curtis and Ayres find in their sample that, "investors incur fees both at the plan and fund level. The combination of plan expenses, mutual fund fees, and menu limitations account for a loss of 10.2% of the optimal risk-premium." So the excess return is on average 10 percent lower because of high fees. They even show that the seeming overweighting of investors into their own company's stock in these plans is not necessarily irrational given the high expenses associated with a lot of the other options in many plans.
It's easy to say, we need regulation! But, this is already a fairly highly regulated industry, and more regulation is not always better.
As always, what would help is better financial education for average people, but this is not easy. Tyler and Alex's textbook has a chapter on investing, but I absolutely could not convince my students that they couldn't beat the market on average. Nor could I convince them that the high returns earned by some managers or funds were likely due to survivorship bias.