I think it has to do with the position of the train in the station as well as the queues that lead to each row, at least that's what I heard someone saying about the one at SFGAm so I'm not sure.
Based on this picture, I also think there's no 8th row because of train positioning.
I mean, I don't get why they they wouldn't put a gate in front of the path, keeping guests from just walking over there when there's nothing there.
I understand what you're saying but to be honest, I'm sure most guests don't pay much attention to it.