Why can't we join groups in the maw?

[Emphasis mine.]

The wording of the post makes it sound very much intended [that the max level Maw requires jumping through hoops to group up] – Why would there be a setting that can be flipped on/off, then left on (in one specific zone) to the player’s detriment unless it’s a design choice?

Horde don’t have an Against Overwhelming Odds quest to do, therefore, less reason to group up and kill alliance with reckless abandon.