A few random thoughts, some of which are not scientifically verified, but are just common sense:
1. NYC has the densest population of any US city. SF is second. But most of the others, I believe, have large suburban - aka “less crowded” - areas.
2. There might not be any direct flights from China to NYC, but there are about one million Chinese visitors each year. And a virus does not care if it has to go through L.A. first.
3. NYC and the NJ cities across the water from NYC are one huge metropolis. Many people from NJ work in NYC, as they are connected by bridges, tunnels, and subways. New York State has about twice as many people as NJ. That said, the NJ cities do not have nearly the population density as NYC.
4. People in NYC are packed into huge apartment buildings. They pass each other in the lobbies, and there is a lot of close walking on the streets. Easy way for human-to-human transfer. And who knows how well the air in those buildings is filtered/conditioned?
5. NYC has a huge number of skyscrapers. If someone sneezes or coughs, the trapped virus will float around in the air until people inhale it.
6. Travel in NYC comprises a lot of mass transit (subways and buses) and taxis. Again, people in close proximity, so it would be easy for the virus to get transferred from one person to another.
Bottom line: NYC and cities in NJ are petri dishes for the transmission of a virus.
Thank you, all good points!