The Withering Branch Monster that was thrown away dared not return to reason with the Demon Tree People; it followed the main army once again, charging forward to hunt new prey.
Their hunting pattern resembles an ant colony, as does their overall structure.
The Withering Branch Monster is at the bottom level of the entire ant colony, akin to worker ants; everything they have is given by the Ant Queen, and their born purpose is to serve her.
At least within the Demon Tree Army, this is the pattern presented.
And the Demon Tree People who snatched the food from their mouths just now weren't soldier ants, but Ant Guards, the direct protectors of the Ant Queen. They didn't enjoy a single bite of the food but worked together to drag it along the rumbling path the Demon Trees must traverse.