Hoping to seal away the Odelates for good, the Prime Diathan retreated from the Material Plane. Behind themselves and their defeated brethren, they erected a barrier known as the Diathan Net, which would prevent any god from physically crossing over into mortal realms.
The departure of the gods from Avada, and the diminishing of their influence, was an event that has since come to be known as "The Severance".
This was not a unanimous decision; some Prime Diathan didn't think creating the Diathan Net was truly in their best interests. But those deities were outvoted. In the end they all believed it to be the best chance in saving Avada.