So that the theme from the fairy tale will attract viewers. The audiences curious to know how when the characters grow up will be like, what will happen, ... very few movie was made in the heyday of Disney derived from the real-life stories. Miyazaki is different, he often based on stories from real-life and created new characters of his movie.
Next, the different transmissions massages: The movies of Miyazaki always carry the message about ecological environment protection ( like "Princess Mononoke", "My neighbors Totoro", ...) but the transmission messages in his movies are not too stereotyped. While Disney almost never works on this topic. Disney also does not intend to touch on the social status (except "Pocahontas"). The messages in Disney movies are often personal meaning, they always advise: follow your dream and be yourself.
Thirdly, The character nature: The villain in the Disney movies always represents evil and there is no remorse. In the episode, there is always a battle between the protagonist and villain, the end is evil will be punished. Meanwhile, the villain in Miyazaki's movies is not often exaggerated, they are always the available quality of repentance in the soul (such as " Princess Mononoke"). Furthermore, not all of Miyazaki's movies appear the villain (like "My neighbor is Totoro", "KiKi-the little