Pretty sure it's because the animators recognize good writing too, having worked on these for as long as they have. I'm not saying King vs Zoro wasn't good. But, where was the emotion, stakes, or drive through that fight. Zoro becoming a King?
Luffy was fighting for the hopes of Wano and a coming of old legends.
Sanji was fighting himself, his family, and had an emotional existential crisis to overcome.
Zoro vs King was ..? What WAS the point of having him take King aside from 2nd?
Animators who work on the anime probably get sick of just action, people want to make masterpieces and effect watchers emotionally, be a part of the history. Not just draw fight scenes because they're in the material.