Really, I think turning them down is a smart move.
Kelly has only been a college HC for 3 years. If I'm him, when I see guys like Spurrier and Saban who made the leap and flopped, I'm going to think about it. When I know I have a sure thing in the PAC-12 and have 200% job security where I am and I have my program setup the way I want it, I'm really going to think about it. When I think about how fucked up Tampa Bay is, both in the locker room and the front office, then shit really starts to become clearer. Maybe he simply knows his limitations, and is more focused on long term than short term, i.e., more than likely being fired by TB in 3 years.