I don't know, maybe in the player being able to control sexual actions of the protagonist as she becomes sluttier and sluttier and abandoning being an angered molestee or lost battle rape victim for becoming an actual porn actress (as in 'the one who takes action')? Why shouldn't freewheeling slutting be fun? Why should anyone even ask where the fun is in having consensual sex, even if it's only as a game player controlling an MC? I know the game relies heavily on the sexual corruption trope, which I personally find harder and harder to accept as it somewhat mindfucks with lewd game consumers by moralizing in a roundabout way, and taking a journey from 'I will gouge your eyes out and throw them in incinerator!!' to 'I have become addicted to cum enemas' takes time, but some players play sex games to play sex, no pretence. What this game offers, which is quite rare in all the sex games that you can find here, is that you can actually play out sex scenes with quite a generous degree of freedom, instead of just passively watching an otherwise 'uneditable' sex scene unlocked as a reward for completing a find-and-fetch task, farming enough trust or pimp points or choosing the right wrong answer. All the sex scenes in KP are executed as interactive 'battles', which you can win or 'lose' and these sex-battles are fully equivalent to 'normal' combat, which means subduing enemies and achieving all in-game goals (maintaining Order, finances and subjugating floors) can be done through sex. Thus sex, albeit arguably avoidable is the driving force of the game. Isn't it fun?
Sure, the sex scenes are repetitive. Come to think of it, sex itself is repetitive, there's only that many orifices, appendages, partners, attires, sceneries and positions to choose from but you make it sound like the non-sexual content in this game is anything to write home about, whereas it is not even 1984 Karate Champ level: Karryn air-slashes and swings her halberd while lifebars under thumbnails of her opponents get shorter and shorter until they finally disappear. Wave 2 and 3 and 4 coming, lather, rinse and repeat.