Could it be?
The choice of the Rapax didn't make sense to the remaining Ancestors. Their greater hatred told them tha the Rapax were just cowards, but the much greater reason told them that this was absolute nonsense. The Rapax were a warring race, they were constantly attacking all of the Domains at once. In truth, they were a bit of an eyesore due to this, however they were so difficult to deal with that none of the Domains had taken action until now.
There was no race that was more prepared for war than the Rapax. From youth, they were birthed on the battlefield and from the moment they took their first breaths they had already begun to acclimate to Anarchic Force whereupon by the time they were mature, they were practically entirely immune. It also didn't help that they were entirely undetectable through usual sensory methods.