I mean, if you got the choice to bed women every day or risk your life fighting, why would you choose to expand your kingdom by personally leading wars against other kingdoms and risk losing your life? That's why you'd get a general or someone to fight for you and take care of your problems, the only problem with this is you'd be giving someone else control of the military, which would later come to bite you in the ass with a coup d'etat or other less savory options. So as a king you'd be practically forced to lead major battles to not shake your rule. Also, as a king, you wouldn't really bed every woman you had in your harem, because if you had over 200 concubines and you tried to bed every single one of them every day... you wouldn't rule for very long. (not enough stamina, build additional pylons). (~ ̄▽ ̄)~
I don't see a problem with people writing about harems, even though I hate them. In the end, it's just a guy trying to write a story, and the story ends up as a harem because the author can't come up with any better motivations for the MC than to collect women for his harem, it's sad, really. 😥 (Sad because the author has no motivations to live himself, and is surviving off of the validation from his readers)