There's a traditional structure in the NFL, and sometimes it takes an innovative person to break through to establish a new normal.
In 1997, Bill Parcells left the Patriots in bad blood. He had renegotiated to have an option to cut his contract short prior to the Super Bowl season, expressing reasonable concerns about his health after two heart surgeries, but used that change as leverage to move to the Jets. In the week leading up to the Super Bowl, culminating with Robert Kraft sending a complaint to the commissioner two days before the big game, it was clear that Parcells was a distraction and he wanted to leave.