As i understand it the M30 Luftwaffe Drilling shotgun was issued to luftwaffe pilots in the event of a plane crash to defend against wildlife.
Ironically in many WW2 games german pilots are incapable of using the drilling.
Perhaps i am unaware of a historical reasoning but i haven’t come across any such thing.
Perhaps it is a balancing issue as well, but if not adding the ability to give pilots a shotgun in their personal weapon slot would be immersive and build authenticity.