There is also the jetBlue factor, already an LCC large presence at JFK.
I would hardly call JetBlue an LCC. They're an LCC for their service level, but looking at the ticket price regardless of service level JetBlue is just plain expensive.
ISP isn't exactly close to NYC. It is over an hour from Penn Station on the LIRR and not a taxi ride away. ISP's catchment does not really extend beyond LI and maybe coastal Connecticut that is very close to the Port Washington ferry.
It's close enough for a low-cost airport. I mean, it's about the same distance from New York as Luton and Stansted are from London and they're successful LCC airports. Even Stewart (SWF) could make a low-cost New York airport.
I see a lot of comments here about why some airports are better than others, but they're all comments of convenience. People seem to forget that when traveling on a budget convenience isn't always your top priority. That's the main difference between legacies and LCCs, where legacies focus on convenience (and charge a higher price for that) LCCs do the opposite. They seek to offer a lower price and if that is done by flying from a less convenient airport, then so be it.
The only question is, where can LCCs get the lowest price? Here's a major difference between Europe and America, where in America major airports are able to offer lower fees due to the economy of scale in Europe secondary airports are able to offer lower fees due to free pricing policy. In other words, they lower the fees in order to attract airlines. In America that's not allowed, in Europe it is. Major airports don't have to struggle to attract airlines, they come naturally so why charge them anything less? Smaller airports need every airline they can get and if airlines want a discount on the fees, then give them that discount. After all, without that discount they wouldn't fly there and the airport would be without an airline.
B6 is moving away from being a “low cost carrier”. It is constantly having similar if not higher prices to the legacies. Sure it has its moments, but nothing like it used to be cost-wise. Still a great airline.
The post is more than just WN. I am also curious about NK or F9 entering the JFK market
Agreed on JetBlue, they're no low-cost airline.
Neither is Southwest by the way. They were a low-cost airline back when they started, but nowadays people fly them for convenience instead of money. Spirit, Frontier and Allegiant are the real LCCs of America. All of them chose Newark as their New York airport, not exactly because of the costs (it's known to be the most expensive airport in America) but because of ease of access. Newark isn't slot controlled, they can get in and the price difference with JFK and LaGuardia is negligible. If it's expensive anyway, what does it matter if it's expensive at one airport or the other?
Still Spirit and Frontier have some operations at LaGuardia. Not that they really need it, after all they got Newark to serve the New York market. But if you have the slots anyway, might as well use them. Then Frontier has some Long Island MacArthur operations and Allegiant some Newburgh-Stewart, but not as much as you might expect.
Anyway, all three American LCCs serve New York. They're just not picky on which airport, after all New York is New York. As a low-cost traveler you can't afford to be picky and these airlines know that.