It could be said that he had invested quite a lot of resources into the black ogre clan to win this battle. Their failure had caused him a big loss that would be difficult for even a being like him to recover from.
"And besides, have you forgotten the entity that lives in the forest? As long as that ancient tree stands, it is nigh impossible to completely capture the forest"
In fact, the real reason why the forest hasn't been occupied by any demons from the Demon continent so far other than the delicate truce was the existence of the protector of the forest.
An Ancient Titan Treant who had reached a very high level and had stopped the advances of the demon time and time again. It was for his existence coupled with a few others that the Ghastly Winding Forest was still standing.
"This…" As someone who fiercely competed with Gekford for the claim over the forest, how could Arctaurus not know it?