Blizzard (the company that owns & operates WoW) doesn't want people to automatically do gold mining, so they try to stop it. A lot of 'gold mining' is "move you character around, click on this pig 10 times to kill it, collect the little bit of money/goods it drops". In order to automate it well you'd have to solve a lot of computer vision problems. Probably cheaper to just use cheap labour.
From my own experience with gold farmers, they have gotten much smarter and efficient which at the same time means it is much harder to automate than the regular WoW "farm bots" that will run around and kill pigs. Also, blizzard actively monitors your PC with the infamous "Warden" cheat prevention.
Back in the "Burning Crusade" days I got an in game whisper (message) with an obvious spam for Chinese gold. I whipped out google and found a few phrases in Chinese and began chatting back, asking where they are from, how are they doing etc.
Sure enough after a couple of tries, they would reply and tell me they were from Wuhan, I believe. Next they invited me into their group, told me to come with them.
They were two Frost Mages and went into the "Underbog" dungeon and proceded to clear the first room with nothing but "Frost Nova", "Blizzard" and "Arcane Explosion" spells - so they kept an absolutely deadly group of 6 hostiles completely immobilized and killed them more or less slowly with "area of effect" spells. But ultimately it yielded them a better result than killing regular monsters would have.
It was absolutely hilarious to watch and help them and it is a very fond memory of an otherwise actually quite boring and repetitive, non-extraordinary game.
And my point being: with blizzard constantly working on making it harder for the gold farmers, they have to constantly come up with new tricks; with the introduction of the "diminishing returns" on root effects, this would not have worked anymore, for example.
