Katsuki hates compliments. He always has, and likely, he always will. It's a side effect of his hyper-intrinsic motivation, you see. Everything he does is for himself, and that's not to say he's selfish, he's not. He just does things because he wants to do them, simple as that. You see Katsuki hates compliments because he hates expectations, and to be the best is an expectation, no? He is the best and he knows that, because he's worked for it. He doesn't need anyone else commenting on that. Katsuki also hates how compliments imply that he was only doing something for the compliment, or for someone else. It goes against the fundamentals of his lifestyle; that he himself dictates his life and no one else. That fundamental is why I personally think so many people who grew up lacking autonomy resonate so much with Katsuki. He does what he wants, when he wants, because he wants to. He represents freedom and perseverance, driving others to keep going forward as he does so as well.