It's because he's a poor fit for this defense. He's not a NT and not a DE. He doesn't have the sand to play NT and lacks the speed to play DE. He's strictly a 3T DT and that's it. Look at his production compared to his cap cost and it's clear why I for one don't see him on the roster next year.
RE: Talib, I've been very vocal in my view that Talib wasn't going to be re-signed either. Like Brockers, his pay vs production didn't warrant it. It's really clear his age is showing and he's not the same ProBowl CB of his earlier days. He was better than Peters but that isn't saying much.
Snead just got a jump on his house cleaning with Talib, and Peters. If his play doesn't improve and I doubt it will, Roby-Coleman is the next target to be released or traded after the season. Troy Hill IMO is on an extended audition. But with Ramsey acquired and David Long waiting, he's a bubble sitter no matter what PFF says. He's a poor man to man CB and is best strictly in zone which is something Wade wants to play less of. Like Nickell, Troy isn't playing like he's being paid. It wouldn't surprise me in the least if they are both packaged to be traded to a CB needy team. With Williams on the team I can see them drafting a CB.
I see the o-line getting a major work over next season as well. Havenstein with a $7.8M cap hit will need to move inside to OG or be traded. With a dead cap of $6.1M it's unlikely he will be released outright. Moving him inside would be the logical move. RG is the most likely place as it will be an easier transition due to muscle memory. With Blythe likely not being resigned it would make sense. Rob would be a clear upgrade. After 2020 if Havenstein continues to struggle he can be traded or released.
This would make the OT's next year Noteboom and Edwards. LG would likely be Corbett or Brewster, with Corbett the most likely. The reason I think it's Corbett is because they traded specifically for him for a reason. He's also practicing at that position now. This would make Coleman replacing Demby as the gameday backup which makes sense as Shelton can also play C. Evans IMO will be the swing OT. So next year's o-line probably ends up like this:
LT Noteboom
LG Corbett
C Allen
RG Havenstein
RT Edwards
Gameday backups: Coleman OG/C & Evans swing OT