Agreed. I think the shorter the avg distance and the more frequent the stops, the shorter the train. Pretty pointless in having a longer train as it would mean that time would be wasted getting on the off the train. Also even if you lengthen the platform, the exits would remain the same and people would gravitate towards the part of the train nearest to the exits.
So instead of having longer trains it makes more sense to have more frequent trains. So not much time is wasted getting on and off train and the time saved means putting more trains on the track.
there is an optimal length based on passenger flow and distance between stations
