Defensive scheme to blame for lack of pass rushing?

[Bengalstripes9]

I maintain that if they knew they were switching schemes this year and that Dunlap wouldn't be as useful, why not trade him last year?
Teams were interested last year at the deadline, but we hung on to him.

Don't get me wrong, I agreed with hanging on to him at the time, because he was our best pass rusher. However, if I knew what the coaches knew, I would have tried to get something for him last year.