Luggage might be one big factor; If someone does not board; their luggage is removed from the hold for security reasons. To do so, safely, would require so muc

Luggage might be one big factor; If someone does not board; their luggage is removed from the hold for security reasons. To do so, safely, would require so much communication between flight and ground staff, that I'm not sure either staff would know how to begin without the middle-ware.