And it's a reason why "just build denser housing" is not a complete solution. More density makes an area more desirable, so prices will remain flat or in rare cases increase since the demand continues to outstrip supply. I believe the solution involves dramatically looser building regulations and major investment in public transit (essentially, get to Tokyo levels of density). Places like SF or NYC are in that uncanny valley of building just enough to keep demand high but not enough to drop prices.