I think people become fans of sports teams because we need something to identify with other than ourselves. We want our moods and happiness and excitement to be based off of something beyond our own circumstances. We can't make life what we want it to be so we blame our TV shows, sports teams, and friends.
It's far easier to put the responsibility on something we have no control over than ourselves. We can't change things around us, but we can change ourselves and that takes courage.