IF we look back at WCI :
Luffy only came to WCI because he can't become PK without Sanji
Judge only survived the Party because Sanji wouldn't let them die
Big Mom was delayed enough for everyone to escape because of Sanji's cake ( and this was kept a secret )
Luffy managed to escape post Katakuri fight because of Sanji and with the help of his family who was only there because Sanji saved them
So basically Sanji is responsible for Luffy getting involved with and surviving the events that earned him pseudo Yonko status, and thus all of the WCI bounty boosts.
Sanji's bounty should have been even higher post WCI to be honest