HOT TAKE: NFL goes through an infinite cycle of offensive and defensive eras.

When RBs dominate the league teams can't abuse cover 2 which allows WRs to score a lot of points. (Offensive ERA)

But since WRs score so much points the RBs get devalued and are no longer good coming out of college which allows DCs to spam cover 2. This shuts down WRs and teams can no longer score a lot of points. (Defensive ERA)

Then RBs value goes up and they stop cover 2.....the cycle continues.......