Originally polygamy was mutually beneficial. In areas where men were killed off early by disease, war, or accident incurred while hunting, gathering, or otherwise providing food for the family, there were many single/widowed women who would see the practical advantage of a communal household with one man at its head. Generally, of course, it would be a rich man, who had enough cattle or fields or goods to provide for a large household, who also had servants to go out and do the dangerous work. Most women would consider it a business arrangement and not get all worked up over the “he likes me better than you” aspect (although such arguments doubtless did occur).
In dangerous times or areas, a husband would provide protection for the women, so women didn’t mind exchanging a single romantic attachment for a practical, realistically beneficial one.
Also, such marriages were often for political purposes. Why did Jewish kings marry more than one woman? Political alliances.
I’ve never seen a meforesh (if anyone else has please tell me!) saying that Mordechai haTzaddik was married to anyone else before or at the same time he married Esther, but that was a marriage of protection, so it’s possible.