User blog comment:Kaido King of the Beasts/Chapter 809: Catfights and Mammoth-Sized Bounties/@comment-7606564-20151204003826/@comment-199.79.169.163-20151204084555

Bounty is directly tired to the threat level of an individual,as perceived by the goverment. A billion bounty means the WG views Jack as an incredible threat. It wouldn't make sense if all that simply came from his association with Kaido.