There are just too many aspects of human language that comprise an actual piece of literature that are not dealt with in a particularly integrated way by current AI/NLP techniques. Narrative structure is a really fuzzy thing in certain respects and has an immense impact on a reader. Symbolism, metaphor, and various idioms are learned through personal interactions and require a sensitivity to the author's role and intended audience.
Of course I just may be out of touch. Have there really been such significant advances in computer generated journalism/writing?