Why would Lincoln Riley leave Oklahoma for the Cleveland Browns or any other NFL team? Why would Riley leave behind a $4.8-million salary (and $20 million buyout) and a comfortable job at one of the premier programs in college football for the uncertainty of the NFL? Chip Kelly.
Despite a failed NFL run and five-year absence from college football, Kelly remained a hot commodity and was courted by several programs, including Florida and UCLA. He took the Bruins job, and though it's not an elite job, it's still a great job with a huge salary. And it showed why Riley and/or Iowa State's Matt Campbell jumping to the NFL isn't that risky.
I broke it down on The Hot Route (starting at 31:32 below):