As with Gurley, it's not just the amount of money, it's timing of the deal.
McCaffrey was drafted in 2017 so 2020 is the 4th year of his original deal.
The Panthers have invoked the 5th year option for 2021, and could have used the tag on him for 2022 & 2023 if they wanted to.
He was already under contract for the next 2 years and the Panthers had control for the next 4 seasons. But they give him an extension now which doesn't even take effect until the 2022 season.
It's the same boat the Rams were in with Gurley: they gave him an extension 2 years before they had to ... and actually cut him before he played a single down for the Rams under that massive extension.
The Panthers probably could have made this deal in 2022. And it's possible McCaffrey won't worth that much 2 years from now ...
AlbaNY_Ram