How do 401k providers compete for customers? (Do they pay some sort of kickback to corporations they serve?)?

The power to invest your money. In companies they do business with. So you get a low yield. But they keep a customer at your expense. It should be illegal to do. Long term you do better just investing on your own. On average. by 2%. Over a 401k. Probably more now. And they can churn them. Moving your money to new plants overseas. And your job with it. Or to buy customer influence.