The old NYC infrastructure and all of the physical work (and permits, contracts, everything else) means a huge overhaul would most likely not be worth doing in dense and already wired places like these.
Also rayiner pointed out in another thread that according to Akamai the US already is pretty high up in the list of overall bandwidth. Also I think the HN / Reddit / tech echo chamber overplays the demand for gigabit internet. Most of America has no need for this, nor the willingness to pay for a connection this fast. 10-25 Mb is fine for most people. Browse Facebook, surf the web, stream a couple of movies, play games.