I think and perhaps CX thinks, that despite the time it takes to travel from Jersey to JFK, those wanting superior service/4x daily choice/HKG onward connections/new J and Y+ will be prepared to make the journey over to JFK. Most people do not fly to and from NYC and HKG that many times a year. Likely twice at most. So making the trip isnt so bad, + they can choose different times of the day to minimise travel time.

This maybe what CX is thinking.... who knows? EWR was perhaps being considered, because they felt there was more growth in the NYC market, but that slots could not be obtained at JFK?