The effect may be the same, but it is considerably easier to set up AVeil in one turn with a ridiculously fast non-passive mon like Sandslash than it is to set up dual screeens in two turns with a slower, passive mon like Uxie or Cress. The ease and consistency with which AVeil got up is so much higher, especially because defoggers can just come in on your double screener 9/10 times and force you out with only one screen or remove your hard work then and there. Not to say that dual screens doesn't have potential, as it just may, but there's usually a reason you don't see dual screen offensive builds spread this far and generate this much discussion.