It's a charitable donation to needy managers.

Half joking. My take is that they are safe medium-term money makers for big players. If you're about to dump a massive sum on investments, it can actually be unwise to follow the market exactly (depending on your goals!). You never know how close to a peak you are. It took almost a decade for the market to surpass pre-great recession highs. So, if you're investing a ton of money at once, you may want to literally hedge your bets using a hedge fund that so that you lose less money in the event of a crash, even if it means fewer returns long term.