^^
Re this:
NIMBYs: Yeah; I can see your point...But so can a cave shrimp.
Victim's families: Perhaps somewhat unfair to cite them as a group as a roadblock to development for a lot of reasons more appropriately debatable in another thread. But in this case, it's irrelevant.
Air rights: All that is part of NYC's arcane and oftentimes convoluted zoning regulations. NIMBYism obviously plays a major role in how things in this domain work out.