Here's why:
* The technology and social norms: The book features technologies like gramophones and early automobiles, but not more modern inventions like airplanes or electricity. This aligns with the late 19th or early 20th century.
* The clothing and architecture: The illustrations in the book depict clothing and buildings in a style consistent with the turn of the century.
* The social context: The series touches on themes of classism, orphanages, and societal expectations, reflecting the social concerns of the late Victorian era.
However, it's worth noting that author Lemony Snicket himself, the narrator, doesn't adhere to a strict timeline. He uses a fictionalized, sometimes anachronistic style, so the exact year remains somewhat ambiguous.