Not going back and reading everyone else's replies, so I may just be restating....
My guess would be that it isn't popular because it sounds like "cola." I didn't know it was popular anywhere, though, so maybe not....
I like the name, oddly. I dislike
Nicole, must mostly because it's overdone and such a filler mn. I cannot count how many people I know with the middle name
Nicole. :\
Nicola is indeed quite similar, but just sounds much better to me.