Why is there a hierarchy or Greek and Roman gods?

In Greek mythology it was Zeus who led a successful challenge against his father, the Titan Chronas who had previously swallowed his 11 other brothers and sisters. When Zeus released them they elected him their leader and he gave each of them a dominion to rule ... !

It's similar to the hierarchy of kings, queens, princes, princesses and nobles in the human world.

Gods reflected the cultures that worshiped them. The Greek pantheon of gods was a family, they were all related to each other. This was a reflection of Greek society, which was comprised of families and extended families. Families do have a hierarchy.

Have you ever read a single Greek myth, if there wasn't a shot caller it would just be an on going myth about bickering gods

That is how things were arranged in those days and still are in many oganizations even today, including some churches and even the military (they call it the chain of command).