Because they are treated that way by those around them. Imagine yourself walking in a place, all look at you, many come up to you just to have you put your name on something stupid as a napkin, and many just want to sit by you. They want you to meet everyone they know just to prove to them they know you (not intimately or as a friend, just because they met you once) and no matter where you go...everyone notices you and come's up to you and wants a picture of you and with you....wouldn't you get a ego that your somehow important? Oh, and if you agree to appear anywhere, they give you $ to do it, because of who you are.
