I think people think that, but it's really not the case at all. I've been told by people that I am above average attractive and random guys come up to me and try to talk to me at my college often. They expect me to be super warm and outgoing like them, but I honestly try to avoid any interaction because of my shyness and anxiety. I really do think people expect you to be outgoing and bubbly if you look attractive. I also think people think shy people are unattractive because many "unattractive" people lack confidence, which can come off as shy.