Except that, unlike the other Harem games, 2 girls came up with the reason for it. The reason is based on Health and Hygiene. They are OK with sharing him with other girls, as long as those girls don't bring other men into the mix, because of STDs.
As reasons go, it's a bit flimsy, but, it's way, way more than what all other Harems have. The MC already had that intention, he wasn't very keen on sharing "his" girls with other men, they just provided him with a "clean" argument.
I, personally, find that Topecita's way of "excusing" the trope, is quite elegant and has some sense, even if it doesn't consider that no "clean bill of health" was required or demanded
before joining the Harem, but, it is, at least, an attempt to give it a spin that isn't based on possessiveness and on a power trip by the MC. Also, none of the girls asked for a "CBH" from the MC, even when they know that he has/had other women.
I know that this is Porn, and uses Porn logic, so, it's not really needed to delve too deep. On this title we have a new approach to the trope, that should be enough, right?
Peace