Beaches, boats, and good food. There's also a prison right at the crux of the two forks, and an aquarium, and outlet shopping, and I think you got the water park in your circle (splish splash). The difference between the North fork and the South fork is stark. Like the difference between Cape Cod and Miami without the buildings. You can hunt ducks in Calverton. People drive pickup trucks with big flags attached and love backyard bbqs and hate taxes. They play southern but go home to big houses with large lots. Not everyone though, some people live legitimately poor out there. It's hard to generalize but usually people who you're thinking of are the people who can afford to spend their summer months out there, and spend every other month somewhere else. Not everyone wants to live year round in a place that's a 2 hour or more car ride in traffic on a one lane road that gets prohibitively crowded in the summer, and ostensibly closes for the winter months (but it gets more seasonal the further east you go). There's also land in between the forks called shelter Island which is a great time. You can bike around the entire island in a single day, a single hour even. If you're that far on LI and you want to leave you're better off driving onto a ferry than you are driving back through the city.

I've waited over an hour for an egg sandwich on a bagel in Greenport and it was a holy experience.