Maybe...he is afraid to go all out. He said so during WCI and Wano.
Perhaps if Sanji goes all out he'll lose control due to some genetic mutation Judge implanted. Like his brothers. Could also be compared to Choppers monster point.
Against Killingham Sanji likely needs to lose control to win by using CoC. In later arcs Sanji needs to learn how to control it by himself, perhaps by learning from Chopper who has similar issues. And until then why not make Zoro knock him out/back to factory settings? You know the line from Wano coming into fruition.
Could also be a good storytelling tool as Zoro would get injured trying to restrain Sanji without cutting him up, thus nerfing himself. Sanji can later deal with the guilt of injuring his crew mate (although to Zoros face he'll gloat about injuring him). And Zoro can, as per usual, be injured going in to the next arc.