Consider this scenario:

Player A: An average defensive player over his career randomly has a great defensive season.
Player B: An average offensive player over his career puts up gaudy offensive numbers out of nowhere.

Player A's WAR from that defensive season will be dismissed by the vast majority as being useless and incorrect, and his WAR will be ignored because of the "bad or incorrect data" being used to measure his defense. Quite oppositely, Player B's WAR will be accepted as hard fact, and his numbers are either considered a fluke or a "breakout" campaign. This doesn't make a whole lot of sense.