The higher/bigger the building, the bigger you need to replace it with, thus it's a much bigger investment, than finding a lot with a smaller building on it.

As a sibling post a bit up mentioned JP Morgan's 270 Park Av. building 215m and it's getting replaced, because in this case it wasn't easier to "just find a lot with a smaller building", which is probably very rare and rather recent (though once there were multi-storey buildings in place of every skyscraper in Manhattan) solution.