Why? Probably because there is no territory marketing departments won't fearlessly course through. The Batman seat features a cape and arm rests styled after the Dark Knight's own arms, complete with hands for cup holders. The Earnhardt Jr. example looks less like the racer himself and more like a generic helmet-clad hot shoe. Still, the treatment doesn't make the product any less creepy.
If you disagree, you can head over to the KidsEmbrace site for a closer look. The seats can be had for around $149 or so. Just don't be surprised if your kid isn't that excited about climbing into a legless crime fighter's lap for a trip to the grocery store.