Their domain had already been nearly conquered, unbeknownst to the protagonists of their world. The only reason their world still exists is due to the kindness of outsider gods like Fenrir Skoll and Cassius Ambrosia, who protected the last land of the living while also refusing to make any further moves because this is a world with no connection to them after all.
Gods are territorial beings. They would not intervene to save the domain of another God unless the former is a close friend or loved one. Because of their overwhelming power and authority, Gods and Goddesses are rarely sympathetic to others and regard mortals as no more than insects.
This is particularly true for an Evil God such as the God of Void. He used to destroy worlds and the only ones he now repairs are the ones his wife destroys while playing. The remainder would be saved or ignored depending on his mood.
