New York isnt the biggest City in the world ( that would be Tokio-Yokohama with about 40 Million people) and the aliens sure dont have the same romantic feeling about NY as humans would do.
Downtown NY is also not a good strategic point for the military.
So the only more or less reasonable solution left would be that NY is the last major City that isnt destroyed yet. But even that lacks some sense. Why isnt New York evacuated earlier ? Why does the military still fight in NY despite that there is nothing left to fight for?
In a nutshell
assuming they got any real intelligence
scew up the economy big time, then take it from there.

Guss
Then that, has got my head spinning in a nutshell.

But, seriously, what could the Cephs benefit from destroying New York City?