The Simpsons - Special Guests by Picture #1

Because Xena can't fly and that's not Xena. And thank you!

I wonder if it's not so much that they didn't try as that Pierce doesn't really have a standout trait, so to speak. He's classically handsome, but so are the vast majority of Hollywood leading men. It was the same with John Cena in his recent appearance. You recognize his voice, but that animation could have literally been any musclebound guy in Hollywood or pro wrestling or sports. Animators will usually focus on unique traits to make characters appear as themselves, not to the extreme of caricaturists, but with the same thought process. With Pierce and Cena, and even someone like Jose Canseco from "Homer at the Bat", there's not much to make them stand out that way, so you hope the voices of the celebrities makes it obvious.