Because SW is in an established fantasy universe full of aliens, mystical powers and lasers.
Little Billy isn't gonna grow up to fly an X-Wing or have lightsaber duels with some antisocial dickhead with a black leather fetish, but he very well could grow up to be shot in the face by some antisocial, terrorist fuck in some god-forsaken third world shithole.
From a mother's perspectve better a son who likes SWs and grows up to like science or have odd hobbies and never sniffs a pussy than one that watches G.I. Joe, joins up and is dead at 20, blown apart with nothing to show for it but a Purple Heart.