How many of these groups were of people who did not grow up with fixed hierarchies, and so had developed organizational skills that did not rely on one?
A hierarchy is the laziest choice among ways to organize.
Hierarchies are places where one relies on many. That is the point of a hierarchy... so that a few can control and rely on many. It is the most unfair way to organize.
It is thus very, very convenient for the few that people are conditioned from childhood to believe it is the only way to organize, and announce it freely in print.
A child is well aware of the parent-child hierarchy that is more or less universal across all modern cultures. You've been conditioned by this book to follow a fringe belief.