both had their careers affected by injuries and/or poor coaching.
Dayne Christ came in as an excellent prospect as a drop back passer. He had one of the strongest arms I have seen. He also had the athletic ability to scramble away from trouble and to pick up yards with his legs. He looked very good as a freshman under Weis, up until a bad leg injury. Under Kelly, he was used in a way that did not maximize his talents, to say the least. Then a second serious leg injury doomed him again. When he came back, Kelly foolishly continued to try to use him poorly. He was never able to recover.
I think that Kiel saw how he was going to be used by Kelly, and that it didn't really play to his strengths either. He transferred and was a pretty good QB at Cincinnati before a serious injury pretty much ended it for him.
The miss wasn't due to the player, but in both of these cases it falls on the coaches for trying to use them in ways that did not put them in the best situation to be successful.