Because its a scientific fact that wherever the words "fending" or "parry" appear in the game, the nearest tank with any semblance of manhood is at least 9000 yalms away from that precise point /sarcasm.
No clue, really. But honestly, its the parry. Tanks for some reason lose all of their ability to think rationally when faced with that stat, and can't muster anything but "ewwweparrry" or "lolrng" followed by *pass* and leaving the instance.
Basically they were all told that if they rolled anything other than "pass" on a thing with parry on it that they're bad and a horrible player, so they have to let shit drop to the floor and make unfunny jokes about how much they hate parry, almost competitively, to maintain a sense of self-esteem as a tank.
