Look, I don't want to start a kink war here, it's both futile and off-topic, but picture this:
You're not very popular with the ladies, have a low self-esteem and you have two possiblities:
a) You play a game that reinforces these inadequacies by confronting you with a very unpleasant situation you'd try to avoid at all cost
b) you make yourself feel better by playing a game where every woman loves you and no other men exist (or at least are no competition)
You don't need to have studied psychology to guess that most people in this scenario would probably pick option b. A is like saying: Hey, I'm allergic to bees, but wouldn't it be fun to put honey all over me?
Now, I'm NOT saying a) doesn't exist, neither am I saying these are the only reasons to play a harem game. I'm actually quite certain for example that one of the reasons is the simple and very gamey fact that people don't like multiple playthroughs, or like you said, it's just a common male fantasy.
I'm just really sick of those "alpha" wannabes who try to make themselves feel better by degrading and insulting people who like NTR and sometimes I comment on that. I'm not talking about anyone in particular here btw, it's just an observation I made over the years on this page.
TL;DR Live and let live. Don't try to analyze people based on their kinks. Reasons to like certain kinks are more varied than: That guy's a cuck, that one's secretely gay, that one has no self-esteem or whatever rubbish people come up with. But much more important: don't judge them based on their kinks.