One factor that effects that anomaly is that the Patriots are always one of the Playoff teams. Since 12 teams make the playoffs and the Patriots can't play themselves, there are only 11 possible playoff opponents for the Pats. Every other team in the league has enjoyed far more down seasons where they didn't make the playoffs.
Our division also contributes to that. The Bills have never been to the playoffs in that time period and even when our 2nd/3rd place teams finish with winning records, they usually lose tie breakers and miss playoffs. Part of that is influenced by how badly AFC East teams are dominated by Pats. Teams that are 9-5 or 8-6 vs rest of NFL only finish 9-7 or 8-8 in AFCE bc they play Pats twice. In other divisions they might finish 10-6 or 11-5 in some years.
Whenever one team DOMINATES, that means the others are dominated. Put the Patriots in any division over the past 16 years, and the story would be the same.