It seems we can also thank it for:

Farmers
Botters
People who generally just don't care for the content beyond a quick stop for whatever they want
Even less knowledgeable newer players, who now have no intent to learn (see above item)
People quick to give up if victory isn't guaranteed (Hint: It never was)

There's nothing wrong with the raw concept of allowing players to level through PvP, but we clearly have people with no desire to actually PvP because they like it, exploiting it for their own selfish gain, and too many others bear the brunt of that. I actually LIKE the idea of PvP offering XP, but if it comes with these kinds of detriments, something's got to give, and as someone who enjoyed it when leveling in order to PvP was my own concern to work out, I can be fine with letting it go for the greater good.