There is a evolutionary psychological rational for why women tend not to have multiple husbands. Women have, undoubtedly, a much more substantial burden in child rearing than your average man will have. Women carry a child for 40 weeks, women manufacture food for the infant, and have developed a generally more nurturing atmosphere that is essential in cultivating a healthy quality future human adult.
This has generally lead women, over time, to be far more picky when choosing a mate, because she is at a natural survival disadvantage if she is left by herself with an infant. She needs to be picky, so she wont' choose an idiot loser who will abandon her, and leave the huge job of raising a new human to only one parent. If she has multiple husbands, this muddies the water concerning who the father of the baby is, and therefore diffuses potential responsibility over several males. Its hard enough getting the actual father to be responsible for his offspring, let alone giving him ammunition to bail if he can claim he is not the father. Thank God women are picky, or we'd probably all be dead!