He's clearly more careful than most estimated. We probably know 1/10th of the total number of times college programs or NFL teams have sent out feelers to him.
Not running a football factory in which academics are a non-factor beyond being eligible is a double-edged sword. Yes, it means you will hardly ever compete for a national championship, but it also means a whole lot less management of miscreant behavior. My sense from multiple comments from multiple coaches is that one of the attractions of the NFL is that you're coaching alleged adults who are responsible for their own behavior and thus you, as the coach, are doing less babysitting, or at least you are not expected to do such hand-holding. It doesn't surprise me that coaches like Shaw, Fitzgerald, Kelly, Cutcliffe have had long stays and have undoubtedly all spurned offers of more money and more recruiting freedom to stay where they are.