It happened in "The Fall of the House of Usher" (by Edgar Allan Poe) that while Usher and the narrator speaks, Usher's sister walks through the room, apparently unaware of the narrator. The narrator's reaction to seeing Usher's sister when he sees her pass through the room was with an utter astonishment not unmingled with dread.
Short/simple answer: because it was forbidden to picture or sculpt anything figurative (i.e. representing a being or object). Figurative art could be wrongly interpreted as a depiction of Allah and worshipped instead of Him, and that would be considered idolatry.
