Well, being someone who can't help but pull a theory out of my Rectal Database, I hearby make the following theory....
...which is mine...
...all mine and completely orginanal....
Orbital Mind Control Lasers that were testing in the early 1970's that affected infants by giving them greater brain capacity to better understand war-games and role-assumption. This was going to be used to turn the whole Generation X (for Xterminators) in to a special bread of dispassionate killers to over run red China and take over the world for Mom and Apple Pie.
Fortunately Gary and co. came up with DnD to fill the extra brain capacity with gaming and not pre-programed killing instructions, and thus saved the world.
-The Luddite