Like I said before, this isn't any last stand for humanity. I guess you could call it the second stand since the mission to stop the king before he hatched failed, but this is still nothing but an effort by a few members of a private organization to do some pest control on their free time. Obviously nobody in the world cares about the North Korea like country they are in right now, either, so even if everybody in it was eaten by ants, the rest of the world would hardly make more than a few headlines out of it. The Zoldyck honchos simply leaving when their part of the mission was over illustrates that further: The threat simply isn't so significant yet that anybody but those directly involved would go out of their way to do anything about it.