Oath Breaking.

PRIDE fate was sealed. It could call for more clones to rescue it, but it didn't do that for fear of losing more. It has already gambled ten clones and lost just because it couldn't bear to lose one clone. It might be better to admit its loss right now. But PRIDE was lucky. WRATH came to the rescue with clones.

This demon god hates PRIDE, but it hates a devourer even more. When demon gods fight each other, at most, they lose some energy. They can recover that energy easily. But a devourer like Aeternus eats their capacity for power. That means they will lose years of work and fall in power permanently. WRATH couldn't allow such a threat to exist, so it joined the fight against the new demon god.

WRATH did this even though it swore to protect Aeternus and not harm him intentionally until the era of conquest. It was willing to suffer the devastating effects of breaking that oath just to get rid of Aeternus.