Campbell can't fire Glenn because he'll be next if he has to fire Glenn. Sure, the very best coaches let go of coordinators all the time from Belichick to Reid. But for a coach as new as Campbell, without any major wins or achievements under his belt, he has no one left to blame but himself if both the coordinators he initially hired end up fired (Lynn and Glenn). At that point, the emperor will have no clothes and if this season goes south in any kind of way, Campbell will be next.
I said it last year and I still believe it. Aubrey Pleasant was scapegoated and fired because the PR of having to fire Glenn would have looked bad on Campbell and meant he was next. It's becoming clear that firing Pleasant did not quite improve our defense the way we thought it did. Today's embarrassing performance highlights that.