I think the thing with Kuon was that he was used to playing with people who didnt care as much as him, so he grew to have a "screw my teammates, I'll do everything myself" kind of attitude. But when he saw his teammates in blue lock fighting for their lives and actually taking it serious, he realized that now he was the one who was bringing the team down instead of his teammates, and he became what he hated. Idk why he didnt have an inner monologue explaining that though, I forget if they do in a later episode.