My 2 cents:
Private equity is a key winner of the ever increased "cost" of going public. Enron, Worldcom and other scandals made the legal pendulum swing hard in investor protection. Quarterly calls, getting hounded by analysts, making the number, lawsuits, short sellers... live is tough for a public company CEO.
As a result, private equity has grown so much, displacing the public markets. With this outsized footprints, it is only natural that returns zone in on the market returns.