The other arguments for why Jinbe has a higher bounty than Sanji (the inflation) sort of fall short when you realize that the same should also be applied for Zoro's case. Why did Jinbe not have a higher bounty than Zoro? If all the knowledge and influence and political power that Jinbe brings or the Warlords getting huge increases then why not have Jinbe be above Zoro? Why keep Zoro above Jinbe even with only 1 mil difference? Jinbe had the highest bounty after Luffy in the crew, he declared joining the SHPs during the wedding ceremony. Sanj had the third highest after WCI. How and why did Zoro jump from the 4th highest bounty in the crew to 2nd and why have him above Jinbe even by only 1 mil?
We already know the world sees the bounties in a crew as an internal hierarchy e.g. Queen talking about taking out the number two's and three's while holding Zoro and Sanji posters or how the Sweet Commanders are seen or even the Beast Pirates.
I think one of the reasons is that Zoro has more notoriety, even Kaido calls him Pirate Hunter during rooftop. One can argue that Sanji being a Vinsmoke also has notoriety but the difference is that Zoro's epithet is earned by his own achievements while Sanji's is due to family connection and he already got the bounty bump because of it with even Queen calling him Judge's son. The last example also puts to rest the assumption that people don't get bounty increases by association. If you are part of something, you have ties to a powerful organization then it is also reflected on your bounty.