You see, there was this thing going on called the Cold War where the West and Communist countries were battling for ideological and technological dominance. You may have heard of it.
The USSR was first to put a satellite in space, first to put a human in space, first probe on the moon, first to do a space walk. But they then fell behind the US in the late sixties and their own N1 rocket wasn't faring so well.
So getting incontrovertible evidence that the US efforts were being faked would have been a massive propaganda coup, both in the Space Race and the larger picture where the USSR was facing off the US all over the world.