After all, even among the Human Race, it's only during periods of great wars that they could afford to strike at Great Divine Transcendents.
In ordinary times, to suddenly assassinate a Great Divine Transcendent, is to forget that they have friends and family. That's not just an assassination; it's a hornet's nest you're poking.
Under the sorrow of the death of a fellow Transcendent, other Transcendents may join forces against the Human Race. When else could you witness the fall of a Great Divine Transcendent? Only in times of great catastrophe and chaos do we see them fall one after another.
Because only in such circumstances do the Transcendents have no leisure to join forces against a common enemy.