User blog comment:12th Supernova/5 Star Wanted Level/@comment-1595565-20140507153559/@comment-10543621-20140514235045

It was probably more of a let both enemies fight it out and reap the benefits sort of thing. If Kaido goes after Doffy, Doffy is done for sure. But Doffy would likely be able to weaken Kaido in the process, which helps in the long scheme of things for them to target Kaido after that.

Of course, Luffy never does things in such roundabout ways. He just deals with each enemy, one at a time. Especially if they piss him off.