The Green Bay Packers know this, and that's why Rodgers' record-setting, $110 million contract wasn't very difficult to get done. The Packers will pay Rodgers $22 million per season because the current salary-cap structure in the NFL just doesn't allow him to be paid much more. This is true in a few ways.
Far below "real value"
Rodgers would be my pick as the best quarterback in football. When you combine Rodgers' age, skill set and experience, I think he's easily more valuable than players like Peyton Manning and Tom Brady. Rodgers makes the Packers contenders every season simply by being there. If there was no salary cap, Rodgers would be "worth" $40 million to $50 million per season easily.
To put it another way: How much would Rodgers be paid if he was a free agent?
If a quarterback-hungry team with cap space like the Philadelphia Eagles actually could get a chance to pay Rodgers, they would spend all of that cap room on Rodgers. They would spend years creating cap room to pay Rodgers.
Relative value to other players
Offensive tackle Gosder Cherilus will be paid more than $15 million this season by the Indianapolis Colts. Rodgers' former teammate, Greg Jennings, will make almost $13 million from the Minnesota Vikings. Offensive tackle Jermon Bushrod will be paid nearly $12 million by the Chicago Bears. How many Bushrods is Rodgers worth? I'd say about 20. On a relative scale compared to other positions, top-shelf quarterbacks are wildly underpaid.
Rodgers' contract also looks reasonable in relation to other quarterbacks. Rodgers makes the same money as Baltimore Ravens quarterback Joe Flacco in the first three years of the contract. On average, Rodgers makes just a few million more per season than Flacco. The gap between their level of play is much greater. The same is true when you compare Rodgers' average salary to Dallas Cowboys quarterback Tony Romo, who makes around $18 million per season.
We're not saying Rodgers should be crying that he's poor. He's being paid plenty for his gig compared with jobs like teaching and police work. But on a relative scale in the football landscape, there is no doubt Rodgers is underpaid.