Unfortunately, the answer to your last question is, because if you don't, someone else will.
More power to 'em. No QB not named Mahomes has won the super bowl while using more than 13% of the cap. Here are the top #s:
2023: Patrick Mahomes: 17%
2024: Patrick Mahomes: 16.9%
2021: Tom Brady (TB): 12.61%
2018: Tom Brady (NE): 12.42%
2015: Peyton Manning (DEN): 12.21%
2011: Eli Manning (NYG): 11.71%
2014: Tom Brady (NE): 11.13%
2007: Eli Manning (NYG): 10.75%
Now compare that to the top QB contracts (by cap %). The asterisk indicates a QB who has clinched a playoff spot this year - I'm including the Rams there.
Burrow and Cousins (although he isn't playing) still have a possibility of a playoff berth.
QB Team Per Year Avg. % of Salary Cap
Joe Burrow Bengals $55M 24.5
Trevor Lawrence Jaguars $55M 21.5
*Jared Goff Lions $53M 20.8
*Justin Herbert Chargers $52.5M 23.4
*Lamar Jackson Ravens $52M 23.1
*Jalen Hurts Eagles $51M 22.7
Kyler Murray Cardinals $46.1M 22.1
Deshaun Watson Browns $46M 22.1
Kirk Cousins Falcons $45M 17.6
*Patrick Mahomes Chiefs $45M 22.7
*Josh Allen Bills $43M 23.6
*Matthew Stafford Rams $40M 19.2
Dak Prescott Cowboys $40M 21.9
Daniel Jones Giants $40M 17.8
Aaron Rodgers Jets $37.5M 16.7
If history holds true, either the Chiefs threepeat, or the Vikings, Packers, Texans or Stealers win it. I'd love to revisit this after the Bowl.
