With the Legend of the Hive, we hear that the BeetleWings and LeafWings (and obviously some RainWings because of the whole venom-spitting abilities thing, ) are fleeing Pyrriah from some reason, and that they could never go back. This was five thousand years ago. You know what else was five thousand years ago? The Scorching. I recon that is what they were fleeing. They must have thought that the dragon race wouldn't survive and would be wiped out by the Scavengers.