Cactusbois don't want Sanji to fight King because their agenda that Zoro is the same strength as first commander level will go down the drain. They know that ZKK is not happening and the one who will defeat Kaido is Luffy, they are afraid that Zoro at the end will just be a support character like Law and Nami when Luffy fought Doffy and Cracker. They don't care about Marco nor do they care about the story progression.