not because of exclusivity, but probably due to someone wanted to be like California, and then every other developer copied the first developer.
One benefit of these "gated" communities is that you don't get door-to-door solicitors. Now, "gated" comes at a minimum in two formats, one, where it is merely a keycode and two, where there is a guard gate. Occasionally the community will have a community center and frequently, it's Vegas, an outdoor pool.