I have a theory on openness and new people. My wife ran the fourth largest gaming meetup in the country for 13 years. My theory is based on that experience.
New people show up. They meet other cool new people to game with and then go form their own groups and we don't see them much anymore, except for cons or LARGE public parties. Except, for a few. Those people so odious that no one can stand to game with. They continue to hang around the public games, meetup after meetup, and you get to "enjoy" them over and over again.