User blog comment:Wirdang/shirahoshi on the picture/@comment-66.154.119.3-20110807144048/@comment-2031609-20110809220519

Well there's that too, but I would assume mostly because of his pirate status. It would potentially make the entire Ryugu Kingdom accomplices to Jinbe's crew and would be considered a threat, which would be the opposite of what they want. Knowing Jinbe, he probably realizes that and doesn't enter FI because of that.