There was no need to humiliate BM and Kaidou so chosen one Luffy can shine even more.
Kaidou, Big Mom and the beast jobbers awaken and the raid fails, the SH manage to escape with a copy of the poneglyph and THAT’S IT, no round 99 bullshit for Luffy, he’s taking those 50 bucks and looks up at the light. Luffy wants to be PK, he’s not ready to face a Yonkou alliance this strong (by strong, I mean before Oda buried BM and Kaidou) have the marines fight the alliance, while Luffy and Blackbeard exploit the situation to reach Raftel.