Defeated, given the current situation of the Human Race, there is still no way to threaten the safety of the Beastman. And given the foundation of the Beastman, even if they are defeated miserably, they are likely to recover much faster than the Human Race by that time. And by then, it's not impossible for the Beastman Tribe to have another opportunity to conquer the Human Territorial Domain while the Human Race hasn't recovered.
Thus, as long as there is a glimmer of hope to achieve their goal of dispatching troops, from all perspectives, those Beastmen at that time did not directly abandon the possibility of action.
So, regardless of whether they can succeed, when things progressed to that stage and they saw how troublesome those Angels were to deal with, those Beastmen still chose to fight.
