Development time is better spent elsewhere. Since Macs are now nothing more than overpriced PCs with a different OS and can run Windows natively, there simply isnt reason enough to spend any development time on a MacOS client. That's my personal opinion, but I would imagine that the developers probably feel the same way.
What your saying sounds like its well informed although its not. They would contract the work out to port the game for osx they wouldn't get creative and coding leads and take them away from the game lol derp. I don't think they do feel the same way as they already mentioned they play on macs.
Theres plenty of demand, heck wow did it.