It takes many months to develop new housing in the U.S. Even when you have local political support, there's a lot of custom manual work and so forth.

It's also very hard to find examples of long-term successful large-scale (town-scale) growth. So we can't just move substantial fractions of people from our largest cities to mid or small-sized cities in a matter of months or years (and get satisfactory results).

Undoubtedly NIMBY forces around the U.S. are partly to blame, but the Covid/WFH exodus is surely the more important factor at this point in time.