One barrier among many to that is the overreach of the preservation movement. Of course I think it was a tragedy what happened to the original Penn Station but the pendulum has swung way way too far. Buildings, blocks, and even entire neighborhoods that don't have much compelling about them at all have had preservation related restrictions put in place. To take a specific example, much of the East Village is downright ugly and is historically significant only for being an affordable place for newcomers to live. The best way to honor that legacy isn't preserving blocks and blocks of four to six story walkups but by allowing a lot more density to bring prices down -- particularly towards the south-west part of the neighborhood where there are more subway options.