My best bet was they just did not stick out to the coaches and the organization felt they could bring in better players who could compete for starting jobs.
Really disappointing to see Denson being released, I loved the guys work ethic but he did struggle with an injury last year if im not mistaken. Im not very surprised about Means, he didnt impress me all too much last season but im sure he will be picked up by another CFL team. Kelley looked like a good ball player but you have to be a VERY talented receiver to compete on this team . The others I have know knowledge of but the team probably wanted to go a different direction and didn't see these guys fitting into their plans.
But it is very possible that a player did ask for his release, who knows really.