I mean, in Harbaugh's situation: You are good at your job. Your current employer signed you to a deal, but you wonder if you are getting paid what you are worth. You would like a better deal. Maybe at your current employer or maybe at another place. You shop around, talk to some people. Go on an interview or 2. Ultimately you decide if you want to give up your good job and good contract for something better. And maybe you can get your current employer to sweeten your deal. Maybe you come to the conclusion that actually things aren;t great out there, and you can be pretty content with what you have.
That's basically what anyone would do if they worked in a field where recruiting and being recruited is a valid part of your work life. Harbaugh is just looking out for himself, which I don't think anyone can fault him for. Michigan was perfectly ready to move on from him if his work didn't improve, so why would he nto be willing to move on now that he has shown that he can still work as well as he can?
On the flipside, if you are Michigan, you see in Harbaugh a great coach who needed a serious prod to evaluate his methods and choose a better path, are you willing to up the ante with him now he's had 2 good years on this path? or are you worried that Bad Jim will turn up again and would you prefer to stick to the contract he has, which is plenty good for someone of his stature.
Both sides have choices to make, but at the moment it's Harbaugh in the driver's seat on those decisions. I'd let him shop around and bring back offers and then make my decision, if I were Michigan, and not blink on his gambits too fast. And if I'm Harbaugh, I'm nto leaving my cushy Michigan job for anything else except an NFL job where I have some control over what's going on. Harbaugh HATED the ending in SF cause he was overruled in personnel decisions and felt he knew better. And he was right, the GM at the time was a complete idiot who squandered mutliple drafts. Maybe Harbaugh gets the god offer from some team, but more likely is that an NFL team will want some control over his work and at least have a functional GM to pair with him. And then Harbaugh has to decide if he wants that and if he can work with the potential candidate.
personally I think that's why the Colts thing hasn't materialized. I think Irsay was quite keen to keep his current GM and his current structure of the GM making personnel decisions and the coahc just coaching. And I think Harbaugh wants to have significant influence on the grocery shopping. Maybe the Broncos give it to him. Maybe the Broncos go with Sean Payton instead. We'll see.