A lot of that is because that is what the defense is designed to do and benefited by their gap alignment. What makes Briggs so great there is that he does make those plays and stops so many plays abruptly in the backfield or at the line.
What bothered me so much was reporters who time and time again prove they really have blinded knowledge was that they claimed Brandon Iwuh played great in the place of Briggs. He played awful for what he is supposed to do. Of course he is going to be unblocked and get tackles because the plays will funnel too him, but he didn't make plays. He had plenty of missed chances to stop the runner at the line or short but let him free or got a little hand on him and trail tackled down the field, that difference was huge in those games and shows the real impact of Briggs, makes one wonder what the Seattle game may have become if Briggs was in to make the stops.