Sitting on $963 billion means huge fees for the Promoters. They get paid in many cases even if they are slow in finding suitable investments. And they have every incentive to put this money to work, whatever the terms, as they are paid on the basis of 'we take (part of) the profits and you investor can keep the losses'. A veritable money-printing machine, built on the basis of leverage and an ever-rising stock market boosted by QE. And no one in the corporate governance and political crowd seems to take notice despite the rising discontent about executive excess in the public markets.
https://www.bloomberg.com//news/articles/2017-09-01/why-private-equity-has-963-billion-in-dry-powder-quicktake-q-a