because King/Queen/Who'Who/Hawkins will confront Sanji en route to the rooftop and i doubt Sanji and Jinbe is enough to fight those 4.
*note : Kid, Killer, and Law is en route to the rooftop too. So we might count them too.
The funny part is Sanji is not too motivated to going to the roof top and fight Kaido. He seems to want to clear a path for Luffy. Jinbei on the other hand seems to expect Sanji to be involved in the Kaido fight. Right now both options are open. Personally as a Sanji fan I'm not too invested in Sanji fighting Kaido in a gang bang. I would rather he faced a calamity or even a tobbi roppo in an all out fight first before going on to the gang bang or participating in other plots that may win the allaince the war.
I like the double meaning of the title. I'm not sure what is the point of the floor system, maybe there will be a powerful enemy in each floor, which will force Sanji & co to stay behind so Luffy can reach the rooftop. Unless it has no particular meaning and Sanji will make it to the rooftop with Luffy, I really can't say. I think it depends on what King and Queen will do. If they go on the roof, then Sanji, Zoro and possibly Jinbe will go up there too.