It's part of the next man up philosophy, and why it seems to work better here than in other instances. In Brady's case it was a conscious decision Bill made to not have him on the sidelines because he didn't want cameras panning or chatter any time Cassel missed a throw. Didn't even want Cassel to see him lurking in those instances. Wanted him to rely on himself and his coaches. Normally a starting QB who is injured will be around to help, and Brady was behind the scenes, but following a season ender as was the case with Brady (and not Bledsoe) they can become fuel in a controversey or undercut the confidence a team (or the player himself) has in a replacement or even interfere with coaching. After a few weeks when Bledsoe was cleared his presence began to spark one, but he also functioned as the #2. And fortunately for Bill the way Brady is wired competitively wasn't going to allow Drew to shake his self confidence or influence him one way or the other. In Bill's book for the most part if you're out you're out.
In a perfect world I'm sure Belichick like them to publicly disappear entirely until they are cleared to play. That seems to be the one thing Gronk has struggled to come to grips with. They were touting him appearing at some local awards dinner on WEEI earlier this week. But maybe the media missed it or he did because I haven't heard a word about it.