Why do the film versions of Frankenstein tend to view the monster as mute and inarticulate?

Mary Shelley's novel Frankenstein is a frame narrative. This structure gives the reader the chance to learn about the nameless creature from his own point of view. He explains to his creator that he has learned to speak and read by watching the DeLacey family and by reading Milton's Paradise Lost. By being able to learn about his wants, desires, and dreams from his perspective, the reader develops sympathy for the monster.
Hollywood tends to omit not only the creature's ability to communicate but also any aspects of humanity he possesses. The novel is timeless as it offers questions about creation, science, and the quest for knowledge that still exist two hundred years after its original publication. Most film adaptations try to fit more into the horror film genre, and so they portray the creature as more of a monster. To fill the role of a scary movie, their monster is usually set only on revenge and lacking any ability to explain the reasons behind his anger. Without the ability to communicate, these movies are able to keep him painted as the unsympathetic antagonist of their movie versions.