Once again I will opine with my best impression of the PSU Oracle.
Christian Hackenberg is still a kid, a very smart, very confident, very talented, and highly thought of kid. No one can know what he was thinking so this is just my two cents; my observation of this kid over the last 4 years.
I'd start off by saying I met Christian with my son at the 2012 Ohio State/PSU game. He was there with some other recruits standing outside the tunnel below the upper decks near the concession stand. It was very late in the game and a lot of people had already cleared out. I noticed him right away and took a football over to get it signed. He was very accommodative, very humble, very young. I looked at my son and said out loud "this is the next Peyton Manning". Christian had a big smile, almost an Oh Golly Gee thing--like I said, a kid.
That being said and also making it very clear that he has done more than his fair share at PSU and will go down as one of the best pure passers we've had here; he, like all of us, is not perfect. Very few could have withstood the withering spotlight he has been under the past 3 years. He has done a more than admirable and far better than adequate job under those conditions. I also believe he is a natural leader.
That being said, this was an intentional slight. Several threads here have accurately listed the missteps and several have made good points on his strengths and the successes he's had under one coach vs. the other. My own belief is that Christian was bigger than life when Franklin first got here. He was bigger than the entire coaching staff and Franklin did a very smart thing by walking carefully around him--that is what a head coach is supposed to do. Donovan on the other hand had one sole responsibility when he got here and that was to make Christian buy-in, make him a believer in what they were trying to do--he never accomplished that.
As many good words Christian had for Donovan and Rahne, the reality is he failed them and mostly because he never truly bought in. If I were to guess the main reason for this slight, it would be that Hack doesn't like the fact Franklin fired John Donovan. But CJF had no choice and it was the right choice. That is the reality which will eventually have to be accepted because it is the truth.
This slight is the kind of move made by a kid, a mistake because it lacks maturity and perspective. Guys like Hack, OB and Franklin are very confident in themselves or they wouldn't be who they are; it is critical to their success. That ego sometimes clouds judgment and mistakes are made because after all, they are only human, so I wouldn't be too tough on him, still, this will go down as a mistake. Franklin did all he could and made the moves he had to make. When performance does not meet expectations there are no other options. A lesson Hack would be smart to learn, the only way he will be successful at the next level is to fully embrace that concept.
This is not meant to be mean spirited or chippy, but if I was a GM/coach at the combine I would ask one simple question. Were you responsible for John Donovan getting fired at PSU? And, Why didn't you mention your head coach in your farewell message? It's fair game, because everything is fair game in the real world. It's a difficult to face the real truth of something so my advice would be to tell the absolute truth and move on. Everyone makes mistakes.