Final answer:
Poe's stories are all dark because of his struggles with alcohol and depression, which greatly influenced his writing.
Step-by-step explanation:
Poe's stories are all dark because of his struggles with alcohol and depression. His personal demons and inner turmoil greatly influenced his writing, causing him to write dark and melancholic stories. For example, his story 'The Tell-Tale Heart' explores the theme of guilt and the effects it has on the narrator's mental state, which may be reflective of Poe's own experiences with guilt and remorse.