The reason is really simple, the story is not a full throttle romance, so you got some sweet bits of that and that girl is not even the main love interest, so its a really slow romance with her, thats like i said before is mostly end game content... the annoying thing about MC x Knight-chan is the MC being really hesitating about her, i mean his trauma over his shitty polygamy-family is really deep, while the relationship with the main girl is pretty solid