A couple reasons Campbell hasn’t left:
1) He would suck at a blue blood and he knows it. If he takes the bigger job, he’s on his ass in 3 years. He has a lifetime contract in Ames, and he’s still making generational wealth. His strength is motivating and developing raw but talented guys. He can’t relate to the higher end athletes, and he’s kind of a shitty in-game coach.
2) He has complete control of this program. The AD lets him do as he pleases. He’s stripped so much traditional coach expectations from this job.
3) He’s a private guy who hates glad handing BMDs and being in a microscope. He’s a huge celebrity in Ames, but people leave him alone. He could take his wife out for supper tonight and no one is going to bother him about that abortion of a football game.
4) His wife and kids love it here. Allegedly his wife and a childhood friend turned lawyer serve as his agent(s).
5) Small expectations. He’s a god for winning 8 games/year. He’s not getting fired for going 4-8.
TLDR; he makes a shit load of money to do a job he loves, in a place his family loves, where there is very little pressure on him.