The Greek city-states or "polis" as they were called would compete against each other in the Olympic games. This event was so important that if two polis were at war with each other, they would suspend hostilities during the games so they could participate in the event. Sports were very important to many of the Greek city-states. In Sparta, for example, even girls would train some physical activities from a young age.
I think it's because they didn't want it to be so easy for someone to step in and issue new decrees randomly. Everyone would need to agree, given that America runs on a democracy.
