But thinking about it, Kaido was insane with the idea of landing the island in the capital; this would automatically trigger the scattered gunpowder and the bombs that basically cause an explosion at the island's level. This wouldn't just kill the fodder, as Big Mom pointed out in chapter 999, but it would wipe out everyone. Lmao.
Unless, of course, Kaido had another way to land the island and prevent these events from occurring. If Kaido was at this level of mental insanity, he would have drowned everyone in the sea, that's undoubtedly Oda's BS.