They do this. Often.
What Blizzard can’t seem to stop is players constantly buying gold.
Problem is bots are tied to players who buy gold so bot banning is no incentive to stop botting anymore than arresting drug-runners is going to stop people from buying drugs.
The only way to solve this would be to, somehow, stop players from buying gold.
Players have no incentive not to buy gold, however. They are given no incentive. In all reality the fact that retail has the WoW Token in addition to China’s Classic servers shows that Blizzard is actually okay with RMT in principle.
While I know what Blizzard’s policy on gold-buying is, I don’t not how strictly they enforce their rules about it. All I need to do is go to the AH and see outrageous prices and I know that’s not happening organically.