1. The Bucs mismanaged Tom Brady's final season
Tampa Bay made a mistake after their first season with Brady and Super Bowl run. They opted to attempt to run it back with the exact same team and it clearly didn't work. Despite the Bucs going on a second-half surge and giving the eventual Super Bowl champion Rams all they could handle in the second half it was clear that this wasn't the same team and changes needed to be made.
The front office responded by bringing in aging stars and failing to fix the run game or obvious issues on the line on both sides of the ball. Tampa wasn't close to the same team both due to these issues and a head coaching change, Brady had one of the worst seasons of his career that ended with a blowout loss to the Cowboys in round one.
It is hard not to think that Tom would still be playing this season if the Bucs hadn't so terribly managed their roster over the past two seasons. Opting to walk away from the game had to be far easier when your team is an obvious dumpster fire that isn't going to be competing for the playoffs again anytime soon.