They offered Jennings a nice contract previous to his last season with the Packers. I don't remember the numbers, but they were around 10 mil. He chose to turn that down and play for the opportunity to get more. Then he got injured, had a subpar season, and probably lost money on Green Bay's original offer.
At the time, and soon after he left the Packers, he and his retinue made comments to the effect that Rodgers was holding Jennings back by not feeding him the ball. He acted a bit like a diva at the end and ended up getting overpaid by the Vikings. Turned out that Rodgers can make a big difference for a WR.
I don't get that air from Cobb. I get the sense that he likes playing with Rodgers and sees their relationship as more of a connection than a competition. Rodgers, too, has made comments about how much he enjoys the connection he has with Randall.
And I think they cut Jones to free up a bit more room to work on Bulaga and Cobb.