The Philadelphia Eagles defeated the New England Patriots in this year’s championship game, postponing their chance at becoming the first team in NFL history to win multiple back-to-back Super Bowls.

It would have been an incredible feat — especially considering how few NFL and MLB teams win back-to-back championships compared to NBA and NHL teams. Since the ABA merged with the NBA in 1976, the reigning champ won the title again in roughly three out of 10 seasons.

[These days in baseball, every batter is trying to find an angle]

There’s clearly a disparity among sports, and while no one can say exactly what’s behind it, sports enthusiasts have theories: