So while EWR and JFK are both in the same NYC catchment area the argument can be made that they serve largely different areas without a lot of overlap. You can draw a line north-south down the middle of Manhattan and there isn't a ton of crossover for JFK/EWR airports. If you live in Suffolk County then you're most likely using JFK/LGA and not EWR, same with Essex county. The NYC catchment area is the most lucrative premium market in the country and UA as a premium carrier likely wants to have a presence east of Central Park. If not? That's fine and maybe AA or some other carrier will see value in a JFK presence, just don't be surprised if UA's future JFK gate plans get rugged from underneath them.