For better or worse, the salary cap has changed the NFL landscape. No longer do teams want to give players huge multi-year contracts, hoping instead to sign them to one-year "prove it" type deals. It's almost impossible for a running back to get paid long-term. Even Derrick Henry from the Tennessee Titans is playing 2020 on the franchise tag because the Titans want to push back having to pay him big bucks. This is becoming the norm with other positions as well, including quarterback.
In years past, general managers would be eager to lock up their starting quarterback to a long-term deal.