I'd say a big part of it, is The Giant attacking the attitude of the average player (and maybe even the average DM) to the average monster.
In that context, the "goblinoid oppression by PC races is real" hypothesis makes the most sense to me as being True. As such, for me, 1. and 2. seem by far the most likely.
DMs stand for "the gods" and "PC races" stand for "the players".