When people move on it does not mean that there was anything wrong at all.....I mean it does not mean that there was a big problem necessarily.
Sometimes someone takes a job and realizes that it's not what he wants to do - unrelated to performance. Sometimes another opportunity closer to the bullseye comes along.
It would be a mistake to assume that someone was at fault.
I can only think of 2 people who left the staff apart from that one example above. The OLine coach who went to the GB Packers and the DLine Coach.
In years where the hawks don't look so good, I'm not going to blame the coach. I'll assume that Iowa just does not have good players.