And it also makes perfect sense that they wouldn't have the military power to clean up the aftermath, with them having to watch for BB, Warlords who are still free (Mihawk is there as well), the Revs and a response from Dragon, Shanks movements and everything else. And now, the power present in Wano (the alliance) has reached quite the level of strenght.
It reminds me of the balance concept and to the arguments "Well if Marine HQ + Warlords = 4 Yonko, why aren't they eradicated already?" and
@Van thread.
Riboku sama also gave a little speech on the balance concept in our dear Kingdom
@MarineHQ62 @Blackbeard @Owl Ki @Fleet Admiral Lee Hung