One can only speculate why. It is clear that the decision was not based on merit. The only alternative explanation is that the decision was made on the basis of political favoritism. While a battle has been lost by the community, the war has not. Public organizing will continue.
Suits are likely to be filed.
There is private property to be acquired on the main parcel. Forest City could have proceeded as soon as that property was acquired. Grid Properties, the developer selected to develop the main parcel, can not. Under the best of circumstances they will need many years to try to find financing. And the community will be able to vote their disfavor in the next elections.