There are ownership problems. People already own the land in cities. If they want to move, where will they go where they can find land? Will they use eminent domain to condemn Farmer John's land so they can build Empire State Building II? (I loathe eminent domain...THAT, IMHO, is a violation of rights, usually for the enrichment of already-rich people.)

And I doubt the Empire State Building will be replaced in the next 100 years. It's already 100 years old. They don't replace skyscrapers often. Smaller buildings, sure.

And that's a LOT of cities, and a LOT of people. Albaby on TMF was always talking about a slow migration of people, but where would they go? You would need to establish new cities, which is quite an undertaking. As I said, first problem is securing the land to build it.