I always assumed it had to do with how they wanted the guest flow directed at the stations. Although, to be honest, I never understood why Epcot has the entrance and exit walkways on the same side of the station, since people exiting Epcot need to cross the path of people arriving to enter the park. I suppose during peak times, most of the traffic would be doing one or the other, but even in the middle of the day I have seen people collide trying to get where they were going. They don’t have the other stations configured that way.