the boys are happy to escape the rules of adults, yet quick to create their own rules similar to the rules that adults create back home.Why?

This is because Golding argues that human nature longs for control. In the boys' case their rules are not always meant for the betterment of the community. The rules the boys come up with quickly lead to the violent and destructive. The positive ones fall by the wayside. This is Golding's point that human nature gravitates towards the punitive and destructive. Most of the boys find this "fun".