Private markets have soared to $10 trillion in AUM. But why have they underperformed public markets?

elon musk (Credit: Krisztian Bocsi/Bloomberg via Getty Images)

I have a riddle for you. 

Or a contradiction, perhaps: The U.S. private markets are bigger than ever, and the source of trillions in company value creation. And, at the same time, for the last several years, the private markets as a whole have underperformed the public markets.