Good question. But even if he does repent of his sins, that doesn't mean he won't rape someone else when he gets out.. People repent their sins, but yet still repeat that same sin over and over..
As Tommy pointed out, he didn't "legally" rape anyone. And she is no help since she stated that she remembers nothing, at all.
So, again, as Tommy said, it seems the judge may have called it right. I just happen to think the law needs some revision.