95% of the country is completely undeveloped. The problem isn't a lack of space, but too many people wanting to live in the most desirable eras. Many people don't seem to realize that the housing boom in the 50s and 60s wasn't people just building these buildings in ultra-premium areas, but building them in cheap, relatively undesirable areas. But the mass of people moving to these areas ended up making them desirable, and ultimately also not very cheap.
This effect was so substantial that from 1950 to 1960 the population of most major cities actually declined [1], in spite of a rapidly booming population!
This is the thing people miss and forget, that there should be natural ebb and flow, but population centers are instead just getting bigger and bigger without really getting more dense.
(It's actually still happening, but people dismiss where it is happening as "suburbs" but if you live in a "suburb" that is 60 miles from "the city" and basically never go to the city, it's really it's own thing.)
Your own example is pretty interesting. From 1950 to 1960, the population of Reno (capital of Nevada) increased by more than 40%! [1] Of course you're right there was also a huge surge in commuting, but people weren't the only ones leaving cities. Businesses also moved outside cities, taking advantage of cheaper real estate themselves, and new businesses also cropped up to service the booming suburban populations.
And IMO this is all a much more reasonable thing to aim for. Density can only take you so far. There are hard limitations and it comes with lots of nasty stuff. I think the only reason things are taking as long as they are to naturally go this direction is because of the hyper-centralization of businesses and seemingly endless low interest rates, making companies with billion dollar valuations quite trite. And at that scale, the long-term cost impact of real estate in an ultra-premium location versus in the middle of nowhere is a rounding error. But monopoly money economics will end, probably sooner rather than later - and it may well end up solving this problem, alongside a slew of others.
This effect was so substantial that from 1950 to 1960 the population of most major cities actually declined [1], in spite of a rapidly booming population!
[1] - https://en.wikipedia.org/wiki/List_of_most_populous_cities_i...