Facebook is wildly successful because its founder matched new social media technology to a deep Western cultural longing — the adolescent desire for connection to other adolescents in their own private space. There they can be free to design their personal identities without adult supervision. Think digital tree house. Generation Y accepted Facebook as a free gift and proceeded to connect, express, and visualize the embarrassing aspects of their young lives.
Then Gen Y grew up and their culture and needs changed.
via blogs.hbr.org