Chazz never uses L & D Dragon in the anime. Strangely enough, the GX anime was being released before the manga. There are even little asides between chapters in GX volumes that talk about how the artist got the job, and didn't want it to be an "animanga." So in Yugioh canon (such as it is) GX manga doesn't really exist.
For one, just because it was used in the manga doesn't make it a major card. Axel uses it, but, assuming he gets added, it's not like Electro's gonna get an animation, and he won't be a level up reward. I doubt Electro will even get a voice clip.
And your point is what exactly? There's a lot of voice lines. The newer characters (GX characters, and a few newer DM characters like Arkana) have a lot of lines for cards that obviously won't be included for a long time, if ever. Jesse has one for Crystal Abundance, and a lot of anime-only cards. Arkana has a line for Pandora's Jewelry Box, a Pendulum Monster.
I used to just think that voice lines meant that a card would come, but now I think that they probably just had the actors/actresses record a lot of stuff just to have the lines ready in case certain cards get released.