I want this too, but the tails represent your favour in Keros' eyes so perhaps he expects more of you to add to your tails. Kiyoko's goes up as she serves her purpose as a den mother, maybe you need to serve your purpose as his champion. If he just gave you the full set, you'd expect to have pretty much met your expected purpose in its entirety and that doesn't quite gel with the notion that you're only part way through your journey as the champion.
Kiyoko gets her final tail at 32 kits, that's a prolific level of kits for a den mother (she can pretty much retire her womb at that point), she has reached a level that all other den mothers would be in awe of, she's earned her elevation to Keros' most favoured. Do you think we have?
I want 9 tails but i don't think it makes thematic sense for us to start off there, even with the champion being such an impressive specimen, they still have further to travel, greater heights to reach and certainly more to do for the god of mischief.