There were three reasons for this. Ted is 85, he lost his senate seat, and there were major errors on the part of the prosecution. Very bad errors from what I saw. The prosecutors on a couple of occasions withheld evidence during disclosure. There were a couple of big items the prosecutors "forgot" to disclose.
At the end of the day, the old man is no longer in power, he lost in disgrace and because of the misconduct of the prosecutors, I like this decision to let him off.