Then why are most “uncivilized” societies have more egalitarian and non-violent than “civilized” ones?

Uncivilized societies engage in violence much more frequently than civilized societies.

That’s the case for individual/personal violence, and also for institutional/mass violence.

Civilized societies are better than uncivilized society in anything they do collectively, be it science, production, or murder.

Since civilized societies are so much better at murdering, the few cases where mass murder does happen are much more significant.

However, such cases remain an exception, as opposed to what is the case for uncivilized societies.

Uncivilized societies may be harmless, but they are certainly not peaceful.

Civilized societies are more powerful, but they yield their power much more carefully.