New York City is a great place to live... until it isn't. I define living in NYC as actually living in NYC. What tends to happen is that you get married and have kids.
At that point, the random things that happen when you live in a city shift from "quirky" to scary. Maybe its your car getting broken into. Or the incessant noise of "Mr Softie" in the summer or fire trucks year round. Or your kid's bike getting stolen. Or paying $7 to go over a bridge. Or being packed in a tight subway car. Or your kid walking to school. Or when your kid gets older, taking the bus and subway to school.
While you're going through that, half of your friends have moved to the suburbs. Your kid's cousins in Long Island go to schools with olympic pools that hand out iPads. They have a big backyard and idyllic quiet. So eventually, most people relent and find themselves with a 90 minute commute to a cul de sac somewhere.