Why were German rape victims blamed?

Because much of the modern progressive narrative has been based on lies, falsehoods and idiocy.  And when that happens, and suddenly there are events that challenge such a flawed narrative, you either admit you are wrong (unlikely) or you begin sounding even more stupid, or worse, doing what you once would have condemned with the righteous fury of a moral crusader.  Lying is more than something that is wrong when it's done to fight the abortion industry.  It's also wrong when an entire global ideological revolution is founded on it.