Blocking scheme appeared to change each of Daryl Williams' years with Bills which may have affected his desire.
He was doing a very good job at RT, well enough to get a new contract, and suddenly he was not performing well and moved to guard with spot work at RT.
Some of his performance grade may have been curved based on his new pay check.
I had same thing happen to me (of course not in NFL) and my attitude changed and when they gave me a poor performance rating in my review I signed my review and then added giving them notice I was leaving to my signed review something they did not expect.