Thing is, one problem with fighting against bots is that it is a never ending process. Who ever has to deal with them has to investigate them first, look at every bit of detail not only in relation to the actions they are making, but also the account, since botting would be using compromised accounts.
And the problem with compromised accounts is that people are usually doing something that compromises their accounts. Phishing scams is one thing that can get an account compromised, but another thing that can compromise an account, and this is probably the major way, illicit gold trades, or purchasing gold for real world money through third party websites. People do not realize that them risking their accounts this way is help feeding the botting problem.
There was an announcement made in General Discussion not long ago, reminding people the risk of buying gold from third parties is against the policies and can risk also accounts being hacked. If players stopped feeding into that illicit gold trade, then there would be less botting happening within WoW because there would be no market for gold sellers.