For starters because even if we took the parallel with the Roger Pirates into account numerically speaking Sanji's CoC would not be required mandatorily, but also because he didn't demonstrate to possess that much of a powerful imo and/or the characteristics of a supreme king/leader.
I recall when he would prefer to marry Pudding and say goodbye to All Blue instead of pursuing his dream. This is something Luffy and Zoro would of most likely never even seriously thought about.
I don't know what kind of arc you read, but I would like to touch on it briefly.
Sanji accepted to go for the safety of his crew .
After receiving the threat, he left Zou to see the situation. At that time, Sanji had no idea what Luffy was doing. Zou, on the other hand, was in trouble.
First aim of Sanji was he told his father that he would not accept the marriage and that this would not happen.
Then,
He was then threatened with Zeffs life and his hands. He had to accept conditions for his crew safety and Zeff's lives.
Then, after reunited Luffy, he said that he would not leave his family (especially his sister, as we saw in flashbacks) and that he accepted to die for Zeff and them. That means Big Mom is a monster . Let me go to die and you abondon here. Sanji know that Big Mom can kill everyone.
I guess you can't fully assess or understand the situation.
You overlook Sanji and Robin's childhood traumas. Even after Robin at Enies was released , we did not see much activity from her . Just like Sanji, because her trauma wouldn't allow it.
Now let's get back to your claim. Given the current circumstances and considering that there is a monster like Big Mom, and Zeffs life and crew safety in danger. Any crew member would do same thing in the same conditions. But there is one feature that distinguishes Sanji from others.
Sanji says he can't leave his family. Luffy also said I know, you are like that. For you, this may mean surrender.
His only passion is safety of his crew. This is the first dream of everyone in the crew. For this, Zoro kneeled in front of Mihawk to be more strong to be protect Captain and crew .
I mean CoC doesn't work with your surrender to the dream things . CoC works resolutely with people's passions. We know that when it comes to determination in that crew, Zoro comes to mind first and then Sanji.
For example ,
Luffy said he found out way to defeat Kaido.
We already know it.
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Yes, conqueror his (inner demons) i.e, Vinsmoke childhood
If you are happy , I hope Oda kill Sanji. :)