I think the rest of the answers are being overly simplistic. Obviously, it's neither a universally applicable nor particularly useful generalization, but it is somewhat of a general trend. Think of how gay boys and gay girls grow up and how they learn to relate to those around them and how that expresses itself later in life. Gay girls (most girls) are subject to the unwanted attention and agression by men throughout their life. Pushing off people you can't stand doesn't make one the most desperately outgoing adult. Gay boys, though, are generally ignored by women and face a totally different type of attention from straight boys. Overcoming feelings of isolation often leads people to be extra, sometimes desperately, 'outgoing' later in life.
Just a thought.