- The mobs in AV are unusually hard for their level, eating/drinking or healing your pet after each kill slows you down.
- They don't drop any white or green items that you can farm for.
- People will be doing quests to tame the mobs you're killing.
- You are more likely to be killed by the opposite faction.
Another reason to avoid doing this is the stigma you will attract for being that guy who queues up to AV at level 51 to get half the exp/hour you could be getting grinding anywhere else.
If you're going to grind anything grind some elementals or some mobs that drop stuff that people want to buy. It's faster than questing and you will have gold for a level 60 mount when you hit max level. You won't die to the opposite faction or piss off people on your team.
Finally, when you're level 60, it's easy enough to get exalted if you play AV at the right times.
