Sometime back in the 1930's, NYC passed a law requiring buildings above a certain height to have setbacks to let in light...
Law was changed in I believe late 1960's to also allow buildings to go straight up as long as they had open space or plazas around them.
Most of the plazas are pretty uninspired.
Sixth Avenue in the mid 40's is a good example ( there are these boring pools of water and open areas etc.).