The ZKK cultists want it to happen for a number of reasons.
1) Narrative - They've deluded themselves to think because Wano is based on Japan Zoro is the MC of the arc therefore he should beat the final enemy.
2) Powerscaling - The ZKK cult hide behind the idea that defeating isn't the same as killing so will say Luffy can defeat Kaido but Zoro has to kill him they say this knowing full well killing Kaido will outshine knocking Kaido out and will go forward to try say Zoro > Luffy.
3) Portrayal - They think Zoro is either equal or stronger than Luffy so in their mind have convinced themselves that Zoro must be seen with his captain always or outperforming his captain. They hate the idea that Luffy is stronger than Zoro which is shown by the level of opponent they are individually fighting which is why they want Zoro to desperately go back to Kaido.
4) Coping - They've spent so long now claiming ZKK is a sure thing they can't see anything else and when it doesn't happen they'll claim shitty writing. Despite Oda spelling it out to them that Kaido is Luffy's opponent. From Luffy telling Zoro to leave to Zoro saying Luffy's got it. Oda went out of his way to have Zoro use his strongest version of the move Ryuma did to Kings magma dragon.
Ultimately it all comes down to fanboyism and reading the story with tinted glasses and a bias wanting Zoro to be the MC and the one who shines the most.
It's going to be a salt mine on here when it doesn't happen.
But I'll be here to...