Something like 10-50 of the population worldwide, depending on where/how you measure, moved from rural areas to cities since WW2. This completely upended the large scale population density situation that had existed for millennia. Also, as I'm sure anyone in California or Texas will tell you, there are 1) only so many good places to build and/or 2) so far someone is willing to commute. There is lots of land available to build on 4 hours from San Francisco at pretty reasonable prices (I looked at a 2.5 acre triangle of land with a seasonal creek on it for $40,000), but nobody will pay $900/sq ft for a house that far from their office, even if they WFH 4 days a week.