There's no tangible reason why this occurred. This was the exact same team and the same staff mostly unchanged from the most successful season in the history of the franchise However, they came into the season looking like a Madden 23 coins ghost of their previous self in utterly unable to display the confidence they had earlier in the season.
There was a huge mental issue with the team of 2016 Panthers. They were broken. The season's opening loss to the Broncos appeared to too closely echo the Super Bowl itself, and from then on, the team didn't play like it believed it could be victorious. After nearly losing to terrible 49ers (who finished with a 2-14 record that this year) the collapse was upon us. The Panthers dropped four straight games, Newton was mistake prone and, every week Carolina looked as if it was trying to dig itself out of the deepest and most dreary hole.
Let's imagine for a minute that the problem for the team was psychological. It's unclear what the record could have been. Even an Super Bowl win could have brought a hangover but at a minimum the Panthers could have played more confidently. This is crucial for the future of 2017 and beyond.
Consistent inconsistency has served as a slogan for the Panthers for as long as the franchise has existed. The seemingly endless rubber banding of soaring highs and crushing lows, with nothing in between. If you had won that Super Bowl, finally getting over the hump, would have made a difference.
The general Manager Dave Gettleman would have stayed with the team in the 2017 season. The Super Bowl would have assured that, which drastically alters the Giants' history too. Without Gettleman it's unlikely that the team selects Saquon Barkley and will instead be selecting Sam Darnold -- which will keep the Jets QB within the same city, but in different colors.
After Gettleman's departure , Panthers began to act as if cheap mut coins they were a team that was running over time.