Mate, those were valid reasons - but not anymore. At this point of the story, bringing up Kaido again - when the world basically moved on from him, not just the alliance - just to let him kill in front of people is illogical from the story perspective. Hell, marines even started collecting the remaining beast pirates (and the admiral destroyed every bit of dignity they had before, even King was merely used as a hypetool to introduce the new admiral).
Well, that's YOUR reasoning why Kaido and Big Mom can't be finished by the eruption, it doesn't mean that Oda has the same intention as well. I know, it's stupid for them to end up like that but you gotta move on. No Kaido awakening - when Kaidobros just wanted to see him using awakening - and no ZKK. ZKK is buried thousands of kilometers beneath Wano alongside the potential of Kaido's awakening.