Yes there is a reason, but it's technical. No way to do both of firing a gunner position gun from the pilot, or a pilot gun from the gunner. So we chose to fire it from the pilots position because there is no way to pitch the plane from the gunners position.
HiTech
Is this going to be developed more in the future? I love the idea of being able to use the periscope to shoot, and if we could shoot and maneuver in it that would be awesome.