> Our school also had an 'upstairway' and a 'downstairway' though where you'd get yelled out for going down the upstair way and have to lap the building to get to the downstairway though so they weren't really about reason.
It may seem like no reason to you, but I've witnessed a much higher flow of people when the direction is set and nobody goes "against the current".
This is one mistake I made the first time I went to Japan: I was going "against the current" at the train station and clueless me was wondering why it was taking so much effort for me to make progress...
Even entrances to some public bathrooms now have a divider that splits people entering from people exiting (you can see this at airports sometimes).