On the surface it is a perfectly reasonable question, as he has several things going against him. Some of them include his age, his salary considering he will not be a starter, and his fit for the new 4-3 defensive scheem.
Edwards was brought in by Nix two years ago specifically to play the 3-4 DE position. He is no where near elite, but he has been capeable, and he has met the need that the Bills brought him in to fill. That was then, now two years later with the team going back to the 4-3 his role is greatly diminished. He will be perfectly able to play in a 4-3 DT role, but with Dareus, and Williams in front of him his field time will be much smaller going forward.
With that in mind the next question becomes, is he worth the money that the team will have to pay him as a depth DT? The easy answer is no. This team is loaded on the DL this year with six players that when healthy, IMO the team thinks can play and start in thier four man front (Merriman, Anderson, Kelsay, M. Williams, K. Williams, and Dareus). Then they have a very strong supporting cast of four additional veteran players that can come in, on a rotationl basis ( S. Johnson, D. Edwards, T. Troup, and A. Carrington). As if that was not enough they currently have seven more players with developemental talents under contract (Moore, Gilbert, Ross, Eddins, Batten, Heard, and Dotson). Yes they have a full lineup on the DL.
The other thing that seems important is the ammount of money they are spending here. It is likely that the team is going to spend above 50M on thier defensive front this year not including Edwards, S. Jonhnson, and seven others on the lower end of the pay scale. With this kind of money being spent it makes sence that the team might try to cut costs on the back side of the depth chart for the D-line.
Age is the other factor, and I dont think it takes much discussion to decide that Edwards is on the wrong side as far as Nix is concerned.
So, with price, fit, and age working aganist him, why is he still here? I think the team would love to do him the favor of letting him go early, if they can but there is one little problem. Injuries, with K. Williams and T. Troup coming off from season ending injuries and not yet fully back to health, it is likely that Edwards will stay with the team for a little longer. IMO when the team feels confident that they have Troup and especially Kyle back in the fold then this roster cut will come sooner rather than later. What do you think?