Since WNSH covers almost the entire market there is much more money to be made selling a format that not only a small percentage and specific geographical area of the market listen to.
Keep in mind that WNSH and WNYL had similar ratings, but WNYL made 2-3 times as much money. That's why WNYL is still on the air. The advertisers have more to say about what formats are on the radio than the listeners. You could have a popular format, but if the advertisers aren't there, it will go away. You simply can't run a commercial station in NYC when your revenues are $2 million a year.