By doing this, SeatGeek seem to be going against the trend of recent years. Why have some forums not only provided Facebook sign-up, but even insisted on it or hid deep in the UI the ability to sign in with a username and password?

Was it just to discourage spammers from signing up, because Facebook has taken measures to ensure that there is a real person behind each Facebook account? Or by logging on through Facebook, did you reveal details about yourself to the forum’s proprietors that could be used for targeted advertising?