This is an easy one. Cities like New York learned long ago that you cannot maintain grass without management in dense urban areas. Dogs especially destroy open lawns, but so do all kinds of heavy use, especially in the off-season.

If you look at spaces like Madison Square Park, the grass is entirely fenced off with mesh and stakes and specific gates are opened (and rotated) to enable use of the lawn at appropriate times. Hamilton Park lacks those barriers and this is the result.