I see some saying that the NFL is more attractive, but why?
He's already won a Super Bowl. That mountain has been climbed. He also has limited say in the NFL. He will be at the mercy of his front office. Success is fleeting at that level no matter how talented a coach you are.
Whereas the alternative is to come to UT, which plays in the SEC, the premier power conference and most cutthroat in college football. He can basically run the program how he desires and recruit who he wants to.The long-term job security prospects are far superior to the NFL. The possibility of winning big at the college level does much more to add to his coaching legacy than being in the NFL again.
More importantly he would have much more control over his success here than he would in Cleveland.
We've seen Pete Carroll coach in the NFL and go to college and win big. We've seen Nick Saban do the same. From Gruden's perspective- reviving and coaching the Vols is far more rewarding and has much more potential than going to the NFL.