The main attraction of money-market funds is their liquidity and their constant share value. But if they have an investment that goes south on them, there's a chance that they could be valued at 99 cents per share, 98 cents per share.
Money funds look very good at the moment, but you don't want to move everything into cash and at some point next year, when the rate hikes are over and the Fed starts cutting, find you've missed your chance to lock in higher long-term rates.