Yea odd that he was active all year and then suddenly the last two games is down. But basically it looks like when they are fully healthy on defense (they are close to that at this stage) their preferred balance is 9 DL, 5 LB, 8 DBs (plus the return guy who is technically a 9th DB).
And as @gonzo1105 said above he does the least of the DBs they have up. Bishop and Lewis play special teams, Ingram can play outside or inside. Elam is strictly a boundary corner so when trying to balance up a gameday roster he is the odd man out.
I still think if one of our boundary guys got hurt and missed a game he'd be the starter as he was when Benford missed the Miami game. But as a backup he doesn't "do" enough things for you to have the flex you need on gameday.