@Galactic Navy Officer
It's called "preselection bias". Women (generally) don't want men that other women don't want. That means that (generally) women would prefer to participate in a harem with other woman than have the exclusive attention of a man who doesn't have other options.
This becomes even more extreme when you add things like wealth, power, fame and feudal society that's constantly at war. 3 wives? I'm surprised that he doesn't have 20 concubines as well, just to make sure that the family has enough heirs.
Spoiler!
Why does Mangabuddy block spellcheck in their comment text fields?
You made me create a browser add-on to fix it.
https://sh.nu/qamkeg