Grimm's fairy tales were originally collected from oral traditions and often reflect the harsh realities of life in earlier times. Disney, on the other hand, aims to entertain and appeal to a wide audience, so they tend to soften and sanitize the stories.
Grimm's fairy tales were not intended for pure entertainment like Disney's. They carried deeper messages and warnings, which led to darker themes. Disney transforms these tales to fit their brand of fantasy and joy, removing much of the darkness.
The main reason is that Grimm's tales originated in a different cultural and historical context. They were passed down through generations and contained elements of fear, morality, and caution. Disney, however, focuses on creating a magical and family-friendly world, making the stories more cheerful and less disturbing.