That's my main problem with the Harem genre, I can't get my head on how a bunch of women (or men) gets so hypnotized by the magic dick of the MC, swear eternal love, gets out of her/his house and fucks the next one that lives one block away. I could make my game an harem, sandboxes are perfect for that, but no, I went on the one LI route, locking the others as soon as a storyline is started.
I think that just comes down to sloppy writing, lack of world-building, and no character development.
The question arises, "how would two or more harem members interact with each other in a realistic contemporary setting? What are their motives and reasons for choosing such a lifestyle that's extremely uncommon and taboo in most of the world? How does this impact their day-to-day lives inside and outside of the harem?"
The answer most developers give is, "they don't interact with each other. Because they like MC. it doesn't." I think that's just utterly lazy and quite boring.
Yes, harems are easier to write in fantasy settings; you can throw multiple reasons like women outnumber men, the reason they outnumber men are that the society was or still is very war based, and the man is more prone to go to war and die in it, therefor the human-like species ended up normalizing a singular guy impregnating and forming a relationship with multiple women. Or maybe the way the species evolved because of this causes more women to be born as fail-safe for the common male population drops. Men can impregnate multiple women or something like that. Or one could go in the direction of more fantasy races that consist solely of women that repopulate by interspecies breeding. In a xenophilic society, this could possibly create a culture of men forming relationships with other women. These are just a few ideas I thought up but there are plenty of others one could create.
And as a part of that, you can write how the harem dynamic works. Do they not interact with each other? (boring + cringe). Is there a hierarchy? Is that hierarchy based on seniority, age, species, or might? Maybe they are equal sister wives? Is it a competition? How big are the harems? Are they large enough that everyone takes a role and acts like a small village with specializations? What role does the guy play? Is the seen as the leader? Or maybe this is a legal or moral obligation and he's forced into that role? If an outside man is effeminate, would he be a harem owner, or would society expect him to play a role as a harem member? Is their intersex/futa species in the universe? What role do they play? There are
SO many ways you can play with the concept. It's honestly disappointing as fuck that most games don't even try to do something like that.
In a contemporary western setting, this would, of course, be way harder, but even most modern games play around with fantasy concepts. But for this idea, let's say it's purely "realistic." I'd say implementing a "real" harem would be hard, but maybe the MC has a cuckquean wife and isn't afraid or encourages an emotional relationship with the vixens. Maybe she trusts them enough because they're friends. Or maybe MC finds his way into a formerly lesbian relationship that went polyamorous. Larger harems would rely on a lot of disbelief but I still think you could make them grounded enough.
Well, that's my rant about why I'm disappointed by 99% of harem games.