So like, I'm just a football nerd right? I don't want anything I'm saying here to be taken as insider knowledge or whatever so feel free to assume I'm a dumb fan with dumb fan opinions. My read is that it's all of the above, but the real problem is college football, who runs it, and where its going. There is no doubt in my mind that some of this is about ego; he thinks the 9ers did him dirty, he longs to win a SB, it kills him that his brother beat him by inches, and yeah on some level I think he figures turning around an NFL team like Meyer couldn't, one-ups going 0-fer against him in college coaching.
Plus keep in mind that he's 59; the track record of the league coming calling for college coaches in their 60's is not very long these days. If he's going back, this is more or less the last train to NFLtown. Furthermore, I don't think you're wrong that this was the best chance we were going to have at a national championship; I don't think TCU was that good and I don't think we're going to be 7.5 favorites in a playoff semi-final game ever again. Harbaugh is a freak, but he does still live on this planet; he knows this too and I'm sure it's a factor in the decision.
But the truth is college football is a hot mess right now, and it's being run by TV networks and a constantly shifting group of conference commissioners and power brokers. The transition to semi-pro football has not at all gone smoothly, Michigan has struggled to adapt to change historically, and there's no sign the pace of change is going to slow down any time soon. Recruiting is hard, NIL and the transfer portal make it harder; and that's without even getting into the fact that the refs, player safety standards, and unequal application of the rules are a sh*tshow. If you're signing up to be a college coach today on a five year contract, you really don't know what your job description is going to be even three years from now.
Everything I'm reading keeps implying that Jim is just sick of college football. Some of that is his ego, some of that is Michigan's insular culture, but a lot of it is the fact that big money and greasy football powerbrokers are playing Calvinball with the sport. I personally don't care that much, but apparently it's driving Harbaugh nuts.
Edit: or that's just the excuse he's floating out there to explain why he's about to bolt on Michigan after promising this wouldn't come up again; you could of course, read it either way, but that's what I'm gleaning from the volume of stuff leaking out of the program right now.