User blog comment:Kaido King of the Beasts/Chapter 836: Man of a Thousand Pounds/@comment-68.41.13.84-20160818141636/@comment-26803131-20160818154220

@Roranoa Drake II I believe that bounties are equal to threat level. So physical strength is only part of the equation. The examples people often use are Robin and Teach. Teach purposely stayed under the radar. Robin's threat level was equal to her bounty the problem was that the WG lied about the reason for her bounty in order to save face. We all know that Robin is a capable fighter but the government does not see her as an agressor so her bounty does not reflect her strength. I say this because her combat power post Baroque Works was much stonger than when she was issued her 1st bounty but it only changed from 79 to 80. That isn't because Robin has not become stronger, it is because she does not go around attacking people. Also I believe that they WG lied because if it was known that a 8 year old could read polygliph the Yonkou would have been after her, making it much more troublesome for the WG. And it makes the WG look like bullies and murderers. Garp said it himself Luffy is not one to go around bragging about defeating Moria which meant a change of bounty due to the defeat would be the WG making him more famous. Raising his bounty would make them and their Shichibukai program look weak which I believe was also stated in the manga.

@Dinosel Luffy did recieve a bounty raise, after the War it went from 300 to 400