[JeremyNT]

You can sprawl further out and you can build infill in sparsely populated areas, but you run up against the reality that desirable areas are going to be expensive because they're desirable, and the cost of demolishing existing multifamily homes to increase density further becomes infeasible in already dense areas.

I bet you actually can find affordable housing in the middle of nowhere / towns where people are actually leaving.

This is not to say there isn't low hanging fruit that market rate housing can help with, and some areas have more room for improvement that way than others, but there's a limit to where that takes you that reveals a deeper problem: we treat housing as an asset that "should" continue to appreciate indefinitely, and we even subsidize people using extensive leveraging to acquire it.