For many Alliance players was really disheartening to see expansion-old allies (Highmountain and Nighborne) turn to the Horde because, as allied races were a new concept no one really expected that something like that could happen, especially in the case of Suramar, the questline was pretty emotional at times and we got involved in the characters' drama, so it was a natural path to feel betrayed that "they chose" (Blizzard decided) to side with the Horde.