Luffy is a CoC specialist, Zoro is not. Luffy has been actively using CoC for 400 chapters longer than Zoro, and Kaido still thought it unthinkable that Luffy would be able to use adv CoC...
Luffy is a haki genius and has internal destruction haki, which Zoro doesn't, despite being a CoA specialist, there is skill transfer in being able to use internal destruction CoA to being able to learn CoC coating...
Luffy had to be hit by adv CoC three times for his haki genius to kick in. Zoro has been hit once, indirectly, by adv CoC.