Oh, boy... let me tell you a tale. The current ZKK is way different than it originally started. I remember when, how and why it started, how it changed and why it changed.
Originally, ZKK was about fighting against Kaido with Luffy
till the end, and then Zoro landing the finishing blow to Kaido subsequently killing him, hence the ZKK. It all started after Kaido's introduction, specifically from this panel...
Back then the hype around Kaido and Wano arc was real, the WCI hadn't happened yet so the big wake up call of the post-timskip was yet to happen. Oh boy, there was so much speculation around Wano and Kaido, thousands of videos on YouTube speculating about Kaido's true power and Wano's greatness. In the midst of that all, people were wondering about how will Luffy defeat Kaido!? Kaido was introduced as "undefeated in 1v1" and people thought that the entire fight against Kaido will be a team effort, that many characters will fight against Kaido with Luffy, but Luffy will be the one to lend the finishing blow because he's the main character. But Zoro fans objected that, they said that Zoro will be the one to lend the finishing blow and kill Kaido.
And that sparked the greatest shit show this community has ever seen... greater than Zoro vs Sanji or Mihawk vs Shanks.
At the beginning Zoro fans argued that Zoro must be the one to lend the finishing blow because Wano is a country of Samurais [swordsmen] and Zoro has to do something over the top great then ever before, and being the one to lend the finishing blow to the "strongest creature alive" was something worthy of the future "WSS." And then a theory came to fruition... this theory argued that Kaido is actually a Dragon who ate Oni DF and became human, and Zoro fans noticed it. You see, at the time Zoro fans desperately needed something substantial to back ZKK up, they were already looking everywhere, and this theory was everything they wished for. Zoro fans jumped into the lore "aspect" and the Ryuma parallel, arguing that Zoro will slay the Dragon above the flower capital just like Ryuma. And pretty soon this fan art appeared where Zoro is leading the fight against Kaido...
At the peak of this movement the most radical Zoro fans even argued that "Luffy will or should fight against Big Mom while Zoro fights Kaido alone," but I digress.
The ZKK movement peaked when Zoro fans realized that the gap–which was already big at the time–was huge between Yonko and YCs, which made Zoro fans even more defensive. Zoro fans had been arguing (they still are btw) for years that "Zoro is equal or stronger than Luffy," and the Wano arc could make or break their agenda. They realized that if Zoro doesn't kill Kiado (which was still about defeating Kaido) then it would almost be impossible to push their agenda, which was already a difficult undertaking in first place. So Zoro fans were ready to die on ZKK heal! They were defending ZKK with everything they've got in most aggresive, stupid and offensive way. But then the rooftop fight ended... after that every chapter made ZKK less and less viable, but Zoro fans bet everything on it, so at this point they don't care how Zoro kills Kaido, he has to kill Kaido in order for Zoro fans to save their face (which is already covered in shit). And that's when "Zoro lending the finishing blow" turned into just ZKK, and now that many pepole don't even remember when and why ZKK appeared, its original form was forgotten, some Zoro fans are now ok with Zoro killing already defeated Kaido cuz they bet their accounts unto it.