Biologically speaking, women are more inclined to have a single partner, whereas men are more inclined to have multiple partners.
The reason for this is pregnancy. When any sex session can result in a 9 month commitment followed by a lifelong commitment to raise the resulting child, it's easy to imagine that the person under such burden will want to have a solid partner to help her through the ordeal and not several dozens partners who will refuse the responsability because it could be anyone else.
When it comes to males, they are under the biological imperative to spread their genes, hence the tendency to want to give a good genes injection to any nearby female. (At least, ones that are attractive, aka that the body recognize as having the potential to make good offsprings).
It might seem absolutely retarded in the context of a porn game, however porn games exist in the context of our societies, so they will tend to follow what people want, which is a harem for the average male.
I am not equipped to speak about what the average female wants, so I'll leave it at that.
PS: Also fuck off with the morals. This is is a website where we have giant hamsters raping women and people fap to that (among a plethora of other game scenarios that deviate greatly from what a society would deem 'moral'), so I think if you're trying to advocate for female liberation, you might not be in the right place.