User blog comment:Kaido King of the Beasts/Chapter 801: Another Game of Thrones/@comment-24536822-20150924124553/@comment-10543621-20150925020624

That's the point isn't it? Robin's bounty WAS higher because she was a greater threat. Sanji's current bounty is obviously the 'odd' one meant to tease us, and clearly it's reflecting whatever he was up to when the sunny crew went missing.

Clearly whatever he did placed him at a higher threat level.