NYC's mecca reputation is valid and it comes from a combo of a lot of things. Gauchos AAU, Rucker, West 4th, Kingdome, MSG, places like Abe Lincoln, Christ the King, Xaverian, SJU (back in the day). Its probably the best place to grow up playing basketball.
still though...much like NYCs rep when it comes to just about everything else, NYC's basketball mecca rep leans heavily on the past. tournaments lost funding, places like Christ the King changed, St. Johns fell off, etc... plus the world is smaller now and kids who are on the path can goto prep academies like oak hill or the place in jersey, move across country to play for an AAU team, and get looks from anywhere in the country. UConn, Nova, and Syracuse still recruit kinda heavily in NYC but not as much as they did back in the day