I see new action/adventure animated series pop up and die all the time. So, it seems obvious the "costs" to create an animated cartoon TV show aren't prohibitively expensive.
WoW has a HUGE backlog of content and storys to pull from so writers aren't that stressed. The characters in-game are already animated, so wouldnt take much effort to transition them to TV format.
7-11 million people to immediately pull from. If WoW could get 10% of this group everyweek to watch the TV show, its a success. 20-30% and its a ratings blockbuster.
So, why not?