There are a lot more full-time DINK households these days (in my own circle of family/acquaintances, at least a third of them would qualify, despite them all be

There are a lot more full-time DINK households these days (in my own circle of family/acquaintances, at least a third of them would qualify, despite them all being 40+), and they're often competing against households with kids that might have at best 1.5 incomes for not just housing but any number of goods (cars, appliances etc.). As soon as there are supply constraints of any sort (and there's been a number recently) it's going to drive prices up to the detriment of households with smaller total incomes, making the "choice" to remain a single-income household not a very realistic/attractive one.