Why bother opening a door when you have a man (or maness) to do it for you. A door has been lost since the event mentioned when a 'visitor' fiddled and it was missed on pre-flight walk around. (NI IIRC) Besides which it is windy and wet far more often then nice weather and the cabin is usefull to doff ones kit (LCJ / helmet / armour / weapon ) whilst keeping warm and dry.