He refused to do what the owner wanted him to do: 1) Tank the Dolphins for a higher draft pick, and 2) meet illegally with Tom Brady to encourage him to go to Miami rather than Tampa.
Billionaires want to be obeyed. That’s why he was fired.
And no matter what the NFL does regarding the hiring process, owners are going to hire whomever they want anyway. They can’t do anything except put up window-dressing, and encourage minority hires. They can’t force these decisions on the owners.