Great point. I know the conventional wisdom is that the RC Mausers were intended to be used by the proletariat to defend against a potential invasion, but that brings up a lot of questions... If the intent was to activate these weapons in an emergency, were there any stockpiles of 8mm ammo near the Mauser storage? It would also make sense to provide at least marginal training to the people if the guns were to be used with any sort of effectiveness, but we don't hear about that having ever happened either. And I believe the USSR did have trained/armed People's Militias (the DDR surely did) that would have provided the perfect framework for such training.
That the only "issued" RC 98k's come from places like Vietnam suggests, to me, that they might have been kept less as an emergency weapon stockpile than as just a general asset. The USSR was, after all, devastated by WWII, and they certainly tended to cart off and hoarde ANYTHING from conquered territory that might later prove of monetary value. These rifles might not have even been reworked and stored by a military or paramilitary agency (BTW, does anyone know where the warehouses where they were found were located? On military bases?) but by a part of governement concerned with trade, economics, or anything.
I certainly would not back any of my conjecture above, as I don't have proof for any of it. But neither, as far as I've seen, does anyone have any solid proof to back the generally accepted explanation behind why these rifles were kept. The truth might always remain a mystery.