It's all of those things I mentioned combined. He clearly doesn't interview well because he's been through that process 2-3 times, I'd bet. He's older. He makes a ton of money now anyway. He clearly loves Chicago. The following are all better options:
Eberflus, McCarthy, Gase, Caldwell, McDaniels, Pagano, Steichen, Sirianni, Bieniemy, Flores, Lafleur, Taylor, Richard, maybe Harbaugh, maybe Riley, maybe Fitzgerald, maybe Rhule, maybe Shaw.
There are plenty of options. I'm not going to get into Helfrich because I highly doubt he gets a HC job.