You're a moron, studies actually find that people in the Northern Beaches are the most content with where they live in comparison to the rest of Sydney and the least likely to want to move.
Further each part of Sydney is appealing for different reasons, some people prefer the culture of Newtown, others the night life and central location of the CBD, or laid back beach culture of Cronulla, some people like the multi-culturalism of the South West, etc. Sydney has a mix of everything and the fact you chose the LNS and Eastern Suburbs as the only places worth living suggests you don't get out much.
The Eastern Suburbs are generally so popular because they're really close to the city and are on the beaches. The lower north shore is generally popular for being close enough to the city and the beaches but having less tourists and being more upper class. It basically breeds tossers.