[PB&J]

I don't take this as a ringing endorsement of the lifestyle... realize that polygyny had sexual benefits for the man only. A woman in a polygynous marriage would be just as restricted to sex with her one husband as any monogamous wife. As always, no man wanted the risk of HIS wife having another man's child.
In other words, what this article is saying is that it is natural for a relatively small number of powerful and rich men to have exclusive sexual access to a majority of the women.