Maybe his knee isn't 100%?
he visited Tampa and reports were he was likely to sign there, although it hasnt' happened yet. He has spent his career as a 4-3 OLB, and has played on both the SS and WS.
How he projects to a 3-4, I'm not sure, but he would probably have to play inside since he hasn't been much of a pass rusher in his career. That might not suit him, as he hasn't had to take on OL and shed as much in the systems he has played in. That doesn't mean he can't do it, just I'm not sure if the Pats feel he can given his track record.