Out of millions of players, even if there are 1000, it’s not statistically significant. The amount of money brought in by these limited number of accounts is negligible. A lot of the botting is done by criminals who steal accounts and use stolen credit cards to “pay” for them. When the card holder disputes the charge Blizzard not only has to pay back the money, but also a fee because of the stolen credit card. So it actually costs Blizzard money to have these cheaters.
Just watch the Customer Support forum after a ban wave. Quite a few posts by players claiming innocence.