It certainly didn’t pop out of nowhere. These things take years of planning, as Extell has even shown with it’s latest projects.
This site is across the street from the Park Central, which at one time had its own supertall tower in the works. That may still happen eventually. But what tgese sites have in common (due to zoning and air rights transfers), would be unobstructed views of Central Park (minus a supertall or two).