An additional thought is that a consumer new to the sport is more likely to pick 12 over 11 speed just because it's both newer and is probably easier to have a sales pitch for. "This is the newest option and shifts just like the other 12spd stuff on the expensive bikes" (ie. 12spd) is probably an easier sell than "this may have one less gear, but it's just as good, if not better" (ie. 11spd).
Also very true about the 11spd cost. I was surprised when I saw how little it has dropped.