He'd prefer to do that yet he doesn't
The plot won’t let him of course... which is a shame because Oda usually has a way of balancing the villainy of the Villains with the restrictions of the type of manga this is
For example Doflamingo’s manipulative nature can’t actually ever affect Luffy that much. At best it lured Luffy to the colloseum but that’s at the start of the arc so it’s not a very clear highlight... And Oda does NOT want to pretend like as if Luffy has actual emotional complexity that Doffy can exploit so Oda has Doffy exploit Law and Bellamy instead... The Arc ends with Doffy manipulating law and Bellamy who Luffy actually cares about and that’s how we can have a psychologically manipulative villain affect a main character who does not have psychological depth to even be manipulated like this
But with Kaido, Oda seems to be having trouble with this... Kaido is about domination of wills and yet Luffy is unflinching in his will so once again, Oda requires an interesting work around that WILL NOT somehow have us believe that Luffy’s will can be broken by beating the shit out of him or whatever the hell Kaido was planning to do.
At first the idea was Moriah. Moriah’s will was broken by having his whole crew decimated so is it possible Kaido kills a strawhat and that’s how his villainy can somehow affect Luffy believably? Nope. 80 chapters of the arc go by without Kaido even as the main villain of the arc and we are just fuckin around with Orochi and it’s clear with the tone of the story that death isn’t an option. (Even Law won’t die, the stakes don’t add up for that)
Then Oda introduces Smiles being given to your crew mates and we think Kid is the example and maybe Usopp could be given a Smile fruit and Luffy’s will will be shaken by such a horrible thing happening to his crew mate. NOPE. Turns out Smile fruits aren’t all as bad as we thought and Killer is fine on Onigashima and Kid barely even remembers that happened to his crew mate so Smiles don’t really matter
Now we are in a bad situation where Kaido just keeps making empty threats and for some reason the plot won’t allow him to even kill the scabbards who are too insignificant to Shake Luffy’s will so who cares? What can actually ever happen in this arc to show that Kaido can in fact break a person’s will? Seemingly nothing