Conspiracy theory time, which I 100% believe to be true.
Robert Kraft did not want to give a 42 year old Tom Brady a fully guaranteed contract. Kirk Cousins becomes the first player in NFL history in 2018 to get a fully guaranteed contract, and you think Brady wouldn't ask for the same after all he did in New England for his final contract here?
Robert Kraft cowardly threw Belichick under the bus by telling the public it was 100% Bill's decision if the Patriots extend Brady. If I'm not mistaken, Kraft always took credit for making the deals that extended Brady in the past. Yet he couldn't step in one final time?
Why in the world would an aging Belichick, who was so close to the wins record, not want to extend Brady and virtually guaranteed himself the chance to break the record? I know there was a narrative that Brady was tired of Bill treating him badly/not respecting him, but for some reason Brady was still asking for an extension? I always took that as the local press buying/selling PR spin from ownership.
Because of Bill's military background, I feel like he believes in a order of command. Since Robert told him to fall on the sword and he was his employer, Bill went with it.
Bill knows how desperately Robert wants to be in the Hall of Fame. I believe this is where Bill is getting back at Robert. Bill has been talking to the Hall of Fame voters and has told them what Robert is like behind the scenes, especially with how the Brady situation was handled.