Oh, I don't know. For whatever reason, I find Thos to be a more subtle, consistent, and carefully-constructed text than most of its sponsors seem inclined to claim. As to what source Matthew and Luke are following, and why, see again MarkG's comment. It arose by the symbolically effective but logically inappropriate introduction of an outside theme. The Chancellor and I are working on that, though these things take time.
Truth has an even slower growth rate than myth.