For all the people who want Kaido to get back up, would that in any way, fix all the shit Oda has done to wano?
Like think about it.
Say ZKK happens, then that means the past 50 chapters of Luffy vs Kaido was meaningless, specifically the part where Oda spent 3 chapters on Luffy charging up a punch.
I'd give the same argument as to why kaido doesn't come back even if ZKK didn't happen and Luffy just had one final round with kaido. Bajrang gun was shitty, but the buildup was there for the attack to take out kaido. It had so much force behind it that it launched Kaido through wano and into a pit of magma.