Well something like 50% of working age Americans have some kind of retirement account, and taking money out of that usually involves capital gains. Two thirds of households own their own homes, and it doesn't matter how nice the house is, if you sell it and move that's a big chunk of money in your bank account that didn't come from Personal Income.

You're right that a lot of people don't have any kind of investments or houses to sell, and I think most of them are in the 20% here that spends less than their Personal Income.