First, carriers move fast.
Second, from altitude you're gonna have to lead the boat a bit. That means flying along the direction of travel of the CV, and dropping ahead of the ship. It will take a good deal of experience nad skill to predict the amound of lead necessary, and if that ship turns, you've missed with the whole bombload.
So, I'm sure you'll find a few CV level-bombing "specialists", but for the rank and file, it'll be way too difficult compared with other techniques, so I wouldn't worry.
Oh yeah, and torpedoes below the waterline.