I can't speak for anyone else but for me it's like this:
1. The kitsune usually talk down to you. There are lots of questions they won't answer in a very satisfying way, and if you ask to know more, they act like you're simply incapable of understanding because you're an outsider and won't tell you. Even if you become their god's champion, the only thing that changes is that they're more polite as they tell you to go away.
2. Adult Kinu is awful whichever way she turns out. Hime's entire personality revolves around pleasing people and she's so formal and "proper" that she just comes off feeling so fake. She doesn't feel like a person, to say nothing of her shit taste in men. Inari actually does feel like a person and her boyfriend is a cool guy, but she's got the attitude of a complete and utter bitch. There's no middle ground between the two and she makes it needlessly difficult to like her, the player's own daughter and the center of much of the kitsune content.
3. If you ever say that something can be improved, that something should be worked on, for example inari and Kiyoko's relationship, they just reply with "it can't be helped". That's it. They just give up and shut you down. They don't try to help themselves and they effectively forbid you from trying to help them. Even if you're Keros's champion, you're just as powerless.
4. There's just nothing there for the player. The only quests the kitsune have are mindless fetch quests and a pointless task to destroy a bunch of puppets. The player doesn't have any influence or impact. Really the pc is just a vehicle to deliver Kiyoko and Kinu and serve as their accessory, if you're lucky, and if you refuse to play that role then you're relegated to errand boy at best and sex tourist at worst.
5. Any quests or tasks that seem like they actually might have some impact on the kitsune are reserved for Kinu. If you care enough to see what happens in the kitsune's story, you have to effectively remove yourself from it and forfeit the role of protagonist to someone else. When you briefly play as Gweyr in the winter wolf quest, you know that you'll regain control and go on to play a role in the story. But when it involves Kinu, it's a quest and a story where you, the player, the character who this entire game ostensibly exists for, do not factor into it and don't matter. You're completely excluded. You're an afterthought that doesn't pop up until the end of the quest when the writer remembers you and then frames it as you being told of something that happened in your absence as a weak way of trying to tie it back to CoC.
All in all, the way that there's so little there for the actual player while anything interesting is made for someone else makes it feel as though the kitsune don't belong in this game. It's like they were originally created for a completely different game, someone's precious little pet project, and for whatever reason that game fell through but the writer refused to let it go, so they just shoved it into CoC2. Now they're trying to keep developing their game as they originally envisioned it despite the fact that it now exists inside of a different framework that, for the most part, it only has the most tenuous connection to.
IMO Tetsuya is the only good thing about the kitsune. But like I said, this is just my own opinion. Good on those who are able to get some fun out of them when I can't.