Because Community Managers are not developers and they can not talk on their behalf without asking them; which in some cases silence can be an answer as well. Any answer in such subjects would only cause unrest in the community; developers and high chairs in the company simply see this and ask CMs to keep their manners.
In short; if such threads would worth its trouble to answer to face backlash, they’d do so already. Trying to provoke CMs generally frowned upon as they don’t have any right to answer directly to such subjects.
Want an answer? Hitch a flight to the Blizzcon yourself this year and talk to developers but most likely you’ll get a made up answer that they repeat for every instances of the same question.