Maybe they've seen enough of McNabb all season to know that he isnt going to get any better, and he is allegedly injured (again). He is aging so they know that there was not much more to get out of McNabb than what we have already seen.
Rex Grossman over Donovan McNabb? Redskins have some explaining to do - Peter King - SI.com
Great article here by Peter King. He basically says that Andy Reid and Mike Shanahan have gave McNabb the thumbs down. Also said that Washington was the only team interested in trading a high pick for the past-his prime QB. Oakland could have got him for a 4th rounder....