Some gaming companies nowadays fail at fighting bots, goldselling and exploiting stuff because they don't have enough ressources alloted to it. Bots are like mosquitoes, you of course can't annihilate all of them but you can prevent a lot of them to annoy people. Besides the obvious and often circumvented automated measures, you hire people and run a bot task force to hunt bots and their methods, to watch ingame activity and ban them on the spot.
A three shift job position can easily remove bots by thousands by just monitoring starting zones, main teleports and places where bots go. Add more people to cover more servers. Bots will come back, they'll get banned again and at some point a balance will be created where you'll have some barely noticeable bots here and there, not swarms of bots running behind each others every second.
And they're being cheap regarding this problem because idiots are in charge of making decisions. I'm not "but they have unlimited money" them, it's a company they're here to make money and managing costs is good money. Letting a problem going rampant and resorting to automated software to solve it is bad money.