So.....you think that they take 20% back from him when the fund loses money? My guess is somewhere, somehow, where there is a fund, the manager, the brokerage or admin gets a cut off the top.
The cut off the “top” is the fund’s administrative fee which typically runs anywhere from 1.0%-2.5% of assets under management. In a way many of them do “take back” the 20% because the amount of the loss gets added to the benchmark the following year (i.e. it becomes a higher hurdle to become profitable). That’s why a lot of HFs close, the benchmark for profitability becomes too high.