Why can't we be friends?

High school has given me a crash course in the world of cliques. Even as small as my school (I go to a school with other home schoolers in case you were curious) is I still cannot escape these dreaded social hazards. I cannot stand cliques and never have been able to, because they are self absorbed and arrogant. They are designed to boost the peoples confidence that that particular clique think are good enough to be apart of their group and make the rest of us feel like nobodies. So I ask to all the high schoolers, college students, and adults in the real world why are we so cliquey?