He is not a scheme fit for the Bills. In college, he excelled at man-to-man heavy press corner and he is still learning McD's defensive zone scheme. The only real way to learn in the NFL is to play and he has been underrepped.
Against Maimi, he played well, and in other games not so well. Obviously, this coaching staff must feel he needs more time in this scheme as the physical talent is there. He is after all the fastest DB on the roster.
Sometimes good players don't emerge in the NFL right away. Take a long hard look at the new Buffalo Bill's #1 CB in Rasul Douglas. Eagles, Panthers, Raiders*, Cards*, Packers*, and now Buffalo. Bills fans complained about giving up a third for him at first. He had 3 turnovers against the Jets, 2 INTs, and a fumble recovery.