Why isn't Spec-ID/FIFO completely automatic by default? The fact such an immaterial determination can have such a financial impact is absurd, but isn't the obvi

Why isn't Spec-ID/FIFO completely automatic by default? The fact such an immaterial determination can have such a financial impact is absurd, but isn't the obvious solution for brokers to automatically do FIFO or Spec-ID based on which is more profitable for their clients? As far as I can tell the greedy algorithm would be pretty straightforward and effective.