I can’t speak to retail, as I haven’t queued up for an AV since somewhere between MoP and WoD. I’m also not in the position to watch a video at the moment. Will do later.
I feel that the “learning to play” and “community” arguments are superficial, at best. While there might be some of that going on, the primary reason why folks are doing this is because it has an advantage, as you pointed out (max HpH.)
Some of these groups may be playing for objectives and ending the game. Others are using these to camp the cave. There is plenty of evidence here on the forums of this, and of repeated landslide victories. Again, people are doing this because it provides them with a significant advantage over those who are not.