People forget that the suburbanization of American cities was a very unique situation brought about by a mix of government policy, rural mythos, and racism.

The current urban migration is basically a reversal to the mean and should be beneficial in the long term.

It was a unique situation. But it was largely brought about by huge pent up demand for housing combined with the relatively sudden the means to meet it.

Racism absolutely played a role in how it went down, as did government policy. But the invention of the modern suburb grew directly out of the events of WW2 making it possible for the US to rapidly build large numbers of homes.

Except that suburbanization in tbe United States began well before WW2 and accelerated in the 60s and 70s, long after any post-war prosperity effect.

People moved away from urban centers because they believed (correctly) that living in dense cities detrimentally impacted their health. This later accelerated in part because of racial reasons.

Housing demand could have easily been met (and was met in Asia and Europe) by building denser urban structures, which is what you would expect to happen if there was a confluence of housing demand, increased wealth, and a general interest in living in cities. There was no interest in the latter, which is why suburbanization took place.

Bad for their health compared to driving all the time? Before indoor plumbing, maybe. Now? No way.