You would think so, but us players really underestimate just how large the problem is.
With something like what, a hundred servers, multiple shards/layers, countless instances, and a multi-billion dollar botting and RMT industry, Blizzard is outmanned, outgunned, and outspent.
They need to work smarter, not harder, to stop botting. Hiring Human GMs to police the game world would be a really inefficient use of their resources compared with how many bots they’d actually stop.
It sucks, I know.