The testers probably got stuck or bored before they reached that point. Judging from some old documentary I've seen, the people in these positions aren't necessarily good at games or very interested in them.
Actually, they are required to complete the games (although in some cases that may not even be possible) before rating them. I don't know how it is today, but back in the 90s it definitely was like you say with the people working there not being interested in games or good at playing them, so they sometimes had to get some kid to play a game for them, just to tell him afterwards that he is not allowed to play it. XD
At least it was like this in the BPjM (which decides if a game gets banned completely), but I imagine it probably was not too different in the USK.