Thing is, in the same arc, Garp was seen throwing punched with massive lightning and even Zoro's attack which ended Lucci ended up with an outburst of CoC. And as you pointed out, Luffy's initial kick also had black lightning in it, as did the White Star Gun. Just claiming Oda was too lazy to draw the black lightning in Snakeman is just granting Kizaru a power level he has not proven to have.
Snakeman is a lot harder to draw, genuinely. Think Oda was just too lazy that's all, panel was super ugly to begin with. I was willing to accept adCoC not being used, but a lack of lightning being used against gorosei pretty much told me, yea it's simply Oda being too lazy.
The Garp, Zoro, and also initial base Luffy kick all were impactful scenes, so the lightning was highlighted. That's my takewaway, in throwaway panels where Luffy's attacks were not going to amount to anything, Oda isn't going to bother, otherwise it makes no sense for Luffy to hold back ACoC against indestructible beings, he admitted he can't damage em.