My wife's answer: "Because NO ONE ELSE is doing the worldwide preaching work" (Matt 24:14)
Keep asking her questions that get her to lead you around in a circle back to her original claim.
Now ask her to support the claim again. The object of the game being to lead her to try and support 1919/1914/607/etc., admit to circular reasoning, agree to keep her cultishness out of your marriage, stop indoctrinating your kids with teachings she refuses to support without resorting to dirty tactics, dishonesty and double standards, or whatever else your goal is.