Is it really? Because I was under the impression that polygamy was dying out here in Asia.

And no, it makes more sense from an evolutionary standpoint for one man to have children with one female, than with multiple females. He can only provide for & protect one female and their children, not for multiple. There is a better chance of raising children to adulthood if there are two parents and children, not one man, many women and even more children. That's too many mouths to feed and protect from Saber toothed Tigers.