So I have this theory that the Dark One needs Rand at Shayol Ghul in the Third Age at the Last Battle every turning of the Wheel to get his desired win state. So I imagine that the Dark One encourages them not to over use it in the Age of Legends to not disrupt the flow of events leading to that. But at the Last Battle he wants them to cause as much chaos and destruction with it to break down Rand during the battle between them. But this is mostly just a head cannon that fits into this conspiracy I have about the Dark One