That's not really true, though. At lower income, you pay the bills, and just have left whatever is (or isn't) the remainder. And when you factor in that medical expenses aren't scalable (I had a moderate set of injuries to my arms in 2022 that lead to care that used about 25% of my pre-tax income for the year in 2023), it's even clearer.As a general rule, that's the case. We typically budget our housing and other expenses a percentage of our income.
We scale some things based on our income (folks with more money spend more freely on groceries, for instance), but that doesn't mean all the other expenses stay the same across income levels, much less across social systems. The math is far more complex than that.