HYSA are also FDIC insured which is no joke. Money market funds are vulnerable to "bank runs" the same way a bank is. There have been times, like in 2008, where you were not able to actually pull all your money out. https://www.investopedia.com/articles/economics/09/money-mar...

I guess technically there is always a risk of 100% loss but in the case of the HYSA that would happen if the United States dissolves. With a money market all you need is a bank run.