I think it has less to do with culture and more to do with a generation gap, I read another article about tribal warfare on Papua New Guinea, and while it has always existed there where historically rules and rituals associated with it (e.g. they could only fight on certain days at certain places etc.) so while brutal the fighting was relatively limited/contained. the newer generations largely ignore these traditions (partially due to missionary activity) and also now have access to metal tools and black-market guns which has made tribal warfare much more deadly than it previously had been.