I was talking about the Middle east 3,000 years ago, not 19th-century Utah. They didn’t exactly have census breakdowns by gender back then, but it’s not a far reach to understand that there may have been times when there were fewer men than women. I agree with you that a culture that considers women property CAN result in polygyny, but that’s not necessarily so; women were pretty much considered property throughout Europe until the last century, but monogamy was practiced de jure (concubinage and having mistresses are other subjects). I also agree with the view that the culture in the Middle East 3,000 years ago saw women as property, but it does not necessarily follow that polygyny was a result of that.
Edit: Back to the OP’s point, if you’re looking for a moment in history when God split the heavens and came down to declare, “All right, you men, I’ve been allowing you to have multiple wives, but from now on you can marry only one woman,” you’re not going to find it, because it never happened.