More than 40% of the building square footage in Manhattan would be literally illegal to build today.[1] Developers would absolutely love to build huge skyscrapers housing thousands. However the city has zoning rules with onerous setbacks, height and density restrictions. The focus on ultra luxury development is a byproduct of heavy handed government regulation.

[1]https://www.nytimes.com/interactive/2016/05/19/upshot/forty-...