Nasus Skin Spirit Fire

Why is it that only the Infernal Nasus skin has a changed Spirit Fire? It seems like the easiest skill to edit the picture of, you know? Just draw something else, done.

Like, even a small change in color from Purple to dark Blue or something would be nice. It's alright if his Q, W, and R all are basically the same, I just think that it would be a small but amazing thing if each of Nasus' skins had a slightly different E animation.