Why does Law having CoC need to be important? Characters can be Conquerors just because
I mean there's always a narrative reason explaining a character having CoC, even it doesn't feel that way. It's never really "just because". Even Kid having it served a narrative purpose, when you think about it in the context of Luffy's rivalry with Law and Kid and the symbolism behind this trio.
Law and Kid are two sides of the same coin, both kinda representing two of Luffy's major traits: CoC and Will of D. So one is a D and the other one is a Conqueror, but Luffy has both because he's the MC. Law getting it would defeat the whole point.
And being both a D and CoC user is incredibly rare, only a few of the most powerful characters in the verse are. Besides Luffy himself, only his own family and possibly one of the 2 big bads are.