I kind of assumed it would rotate automatically based on where the person is speaking from? isn't that a missed trick? or too hard to get right?

It was heavily rumoured. Maybe they disabled it after the negative reactions to the Apple Watch always listening feature. Can't have too many issues at once.

I'd love to have that for video calls. No more trying to find a salt shaker to prop my iPhone / iPad on.

That would creep me out if it followed me as I walked around the room.