A big one is people are probably living in higher densities than the data assumes, eg the housing budget for a living wage assumes 1 single adult will live alone in a studio. In my younger years, I knew a lot of people who were sleeping like 3+ adults in a 1 bedroom in NYC, which obviously not ideal but people make it work if they don't have the money:

"The FMR (HUD Fair Market Rents) estimates include utility costs and vary depending on the number of bedrooms in each unit, from zero to four bedrooms. We assumed that a one adult family would rent a single occupancy unit (zero bedrooms) for an individual adult household, that a two adult family would rent a one bedroom apartment, and that two adult and one or two child families would rent a two bedroom apartment. We further assumed that families with three children would rent a three bedroom apartment (the adults are allocated one bedroom and the children two bedrooms)."

https://livingwage.mit.edu/resources/Living-Wage-Users-Guide...