are these areas with declining populations and rising housing prices increasing the number of houses? it could be that the population declines because no one can afford to live there however it's still a desirable area so prices remain high. cities like Austin are seeing reduction in housing prices despite population increase due to construction of new housing.

That only covers a portion of the population. Don't forget the middle of nowhere towns that refuse to tax their citizens (but eat grant money like pigs) and refuse to allow new housing. All of this is essentially being done to maximize property value and keep new people out. This is why people are moving to cities in the US. Not a desire, but a need in order to make ends meet and get on the property ladder.