Because Pixar movies are well done and made in a more sophisticated style that can be enjoyed by adults. There is a difference between making a film for kids and a film that panders to them. Wizard of Oz, Wall-E, and Star Wars are all examples of great kids films. Clone Wars is an example of a film that panders to them.

Besides which, its not even a well-done one. Surely you cannot be comparing Wall-E with Clone Wars? The difference between the two films is the difference between Star Wars and Wing Commander.