User blog comment:Staw-Hat Luffy/Why Kaido?/@comment-4374114-20130204184553

I'm sure there are things enticing about Kaido that is attracting Law. One idea is he may be the strongest creature but that is just one person. BM's crew may be far superior in numbers that would make it too difficult or she has too many paramecia/logia users. Zoans COULD be easier to defeat, as outside the Mythical they have no special ability that could save unexpectedly once the animal is known. Also looking back for comparing to Shanks, Kaido couldn't even slow Shanks from getting to Marineford for WB.

My personal thought on why Kaido first, Oda is leaving the story line open for BM to get beat down more by Kid and the crew. So that way when Luffy and Law are complete with Kaido there will be little of BM's crew left for them to fight through to take her down personally.