I guess it wasn't all about the Shula record after all. It certainly surprises me that wasn't the be all end all for him, but as I commented earlier in this thread, BB is wired quite differently from a lot of us, and at the end of the day I think he just wants to be a coach doing coach things and accepts that the NFL is probably not for him anymore.
I think the issue for the NFL owners is quite complex, they know he can coach defense well at this point, but offense puts butts in seats and his last 5 years he failed to show he is on top of things on that side of the ball. Perhaps he just became too accustomed to delegating to McDaniels. I feel like the same is true as well for special teams. His age has to be a major factor for the owners as well, they can't see a guy north of 70 leading them to multiple championships. Can you really blame an NFL owner if they looked at both of these things and decided it just wasn't the right fit for their franchise? I can't.