It could also be fewer people are willing to start a family because of the cost of a certain quality of housing, amongst certain other minimum standards of quality of life.

For example, people might have been willing to raise kids while sleeping in a single bed in a single room apartment, possibly having to move multiple times.

Now, you only have kids if you can secure a single family detached house with multiple bedrooms located amongst other similar or higher socioeconomic class neighbors (good school district), and at least one parent has reliable employment with health insurance benefits, which might mean living in a metropolitan area with limited housing supply.

True, but even in cities that had affordable housing there was a decline.