Why? Is there a shortage of skyscrapers in NYC? Amazing city, but last time I visited somewhat overwhelming with the huge buildings and large crowds. Train stations are scary crowded. Out west, there is lots of open space unlike the northeast.
By the way, NYC isn't even close to being fully built up. Yes, they will need to improve upon existing and build new infrastructure but can easily double in size over the next 20 years. I would like to see over 1,000 buildings over 2,000 feet tall in Manhattan. Hope I live long enough to see it.
The boroughs are also getting built up. Skylines are developing quickly in Brooklyn and Long Island City (Queens).
I think this would be a great place for Apple to build an East Coast HQ. Something spectacular. Maybe they can buy the MetLife (formerly Pan Am) building, pull that eyesore down and put something in its place.