A big part of that decision is honestly that we live in a very old house, and a few times we have needed to buy new appliances or pay $10k+ in a ≤24hr. emergency, so we try to keep roughly that amount as liquid as possible. Since that’s earning zero and the MMF is nearly as liquid as savings, we just keep all the rest in the higher-interest options, and none at all in a traditional savings account. It’s just been the most convenient and highest yield, lowest risk, most easily liquidated option, with the ease of liquidity cutting minimally into returns while MMF rates are so high.