"Is this a harem?"
Wise Man Say: "No, young padawan. This is a Cluster Headache."
It's just a lazy writing vehicle to make the MC Popular with Wimminz, while at the same time ensuring any possible actual romantic development gets cockblocked by all the women vying for MC's Special Attention.
You rarely see realistic polygamy.
Moonlit Journey has about the most realistic representation of the possibility, and there the position of being 2nd/3rd wife and up is purely opportunistic and outright gold-digging...
Some others in the empire-building genre where it's mainly political ( and the wives quite often compete for position/power....)
And the worst part... IF the girls somehow Get Along and all be Frenz, this means that they can and will gang up on you to have their way.....
Good luck with that...