I think it was because in ARR, WAR was notably more involved of a tank than PLD, and was more wanted for doing difficult things like speed running. PLD was a roll your face on the keyboard and be a tank class, warrior took more finese.
DRK may end up being that now once they end up getting buffed into something useful, so warriors feel a little threatened. Its been interesting to see all sorts of tank boasting on the forums when you can kinda tell the boasting is based off of judging the other tanking classes based on how they worked in ARR, rather than in HW.
