> The US has mind-boggling amounts of land available. What's changed is the ability and desire to build on it.
Times have changed and most people don't want to live in marginal lands that are available in mind boggling quantities. In addition, the reason that a lot of cities were built a few generations ago in the hinterlands was because manpower was needed for resource extraction industries, which have since either become highly automated or fallen into secular decline. We are no longer a nation of farmers and miners.
> most people don't want to live in marginal lands that are available in mind boggling quantities
That's not "times have changed" -- people have never wanted to live on marginal lands, that's why the government paid people to move there.
> a lot of cities were built a few generations ago in the hinterlands
Few cities are built in the hinterlands for the purposes of resource extraction; cities grow where trade is, but yes there are definitely towns that have vanished because we don't as many farmers and miners.
The SF Bay Area is dominated by single family homes on large lots. Yes, SF proper has a high density, but the surrounding areas really don't, and not for lack of demand: developers who would build more housing are literally stymied at every turn, and this is not an accident, it is an intentional plan to reduce the availability of housing and keep it expensive, to avoid "traffic", "crowding", and "changing the character of the neighborhood".
Times have changed and most people don't want to live in marginal lands that are available in mind boggling quantities. In addition, the reason that a lot of cities were built a few generations ago in the hinterlands was because manpower was needed for resource extraction industries, which have since either become highly automated or fallen into secular decline. We are no longer a nation of farmers and miners.