Unfortunately Activision/Blizzard views bots and gold RMT’ers as “paying customers”, just as they do with all their subscribers. Can you imagine how badly it would affect their second quarter earnings statement to actually ban the hundreds of thousands (if not millions) of people who bot, buy/sell gold, or otherwise exploit the game?
It just isn’t profitable for Activision/Blizzard to police their servers in any meaningful way. Besides, keeping IN the RMT’ers allows them to justify bringing in the WoW token to “combat” it. 
Thanks.