I understand this concern, and it is valid, but maybe not for the reasons you think. World of Warcraft is a big world. Huge, in fact. It has many races, cultures, and peoples, and should, in theory, be plentiful enough and adaptive enough to tell stories without using the same material over and over again, and in the same way. In other words, the world should be expansive enough that Blizzard doesn’t need to keep resorting to villainizing the trolls to tell stories of conflict and fanaticism. Of course, this might not be true, even if it should be, but that is a problem with Blizzard and their writers. It is an issue with their limited capacity to create compelling narratives or to create new and interesting villains. The victims of this, inevitably, end up being the pre-existing factions, which are constantly reused in the same way because Blizzard can’t create something new that is equally compelling.