I don't even get the point of bots for something like Hearthstone. I can at least understand WoW or Diablo which have a lot of grinding built in to the game play, but what the hell does a bot even get you in a game like this? The only thing you can do (that I'm aware of as I don't play either) is play the card game.
As far as I know, it's mostly just ego-boosting and stems from immaturity -- they get to feel superior to the other players by beating them and they sometimes record clips or take screenshots of their "accomplishments" to brag with to their friends. It's easy to dismiss the fact that they are using cheats, I've met many a cheater online over the years who keep deluding themselves with claims like "I only cheat because it's possible, I don't even need cheats and I would do just as well without because I am just so skilled!" There's not much you can say when a person 100% believes their own lies.
Personally I don't think they should ban the people who use the cheats though. Instead, just put them in a special area where they only get to play other cheaters or they programmatically lose 90% of their games and just end up raging harder.
Yeah, I actually find it surprising that Blizzard hasn't done this already. Just lock all cheaters on cheaters-only servers without telling them and depending on the person and the circumstances it may even take them a while to notice what happened.