Polygamy more often means polygyny (multiple wives) but in some rarer instances it means polyandry (multiple husbands). In polyandrous marriages, the husbands are most likely brothers. They have one wife in common. If a man can't be a father, at least he can be an uncle. One of the goals in such a union is to limit offspring due to scarcity of resources (land, etc.).
Most polygamous cultures or cultures that allowed it seem from my reading to have polygyny - more than one wife per husband. I didn’t know that word.
Even in ancient Hindu culture or Vedic culture it was mostly royalty who had multiple wives - they could afford it. I never read of multiple husbands in the OT, not that I am a scholar!
that was found only in ONE perhaps two cultures and is village level rare. as in dying out.
Multiple wives still provides the norm because it was entirely based on children or preventing widows from starving. It provided legal protections for the children of those offspring. It was not the cutsey delusion of the harem.