One possibility is you're TOO good looking. Speaking for myself, I tend to stay away from women who are what I call "beauty queens" aka "princesses" aka "women who are out of my league". Another is that you have a disagreeable disposition or look unapproachable, which is harder to pinpoint.
But you might want to take the initiative yourself, whatever the case. That is, if there's a guy you look, make the first move.