Different sports have come and gone. Not all sports are included in the Olympic games and at different times they are being included or discarded. Baseball is no longer an Olympic sport, nor is polo or tug-of-war.
Further Reading:
-http://www.olympic.org/content/the-ioc/commissions/olympic-programme/past-olympic-sports/
Further Reading:
-http://www.olympic.org/content/the-ioc/commissions/olympic-programme/past-olympic-sports/