Because as second-class allies, they all knew about this matter—
They knew that the Goblin Legion would descend.
Thus, the other first-class allies or third-class allies, especially those on the verge of natural decay, would do everything in their power to fight the Goblin Legion to get the scores, so they could preserve the fire seed of their civilization and let it continue.
This was also why, even as Reincarnates, they knew that this would be a fierce battle, but there would still be so many Reincarnates going to wage "war" because—
Too many third-class allies had already hit rock bottom, and even if all the Reincarnates perished, it wouldn't change the status quo.
This had an extremely high probability of being their last opportunity!
After a brief exchange of information, they went their separate ways, each making their preparations—
To hide in the rear during this war.