There is more than one option. 1) Dan Grankowski is not even good enough to be an emergency backup. 2) Dan Grankowski is injured. 3) Mills isn't useful as a blocker, and we are better off activating a better Special Team against Buffalo. 4) Mills isn't ready to contribute. 5) The game plan against Buffalo wouldn't use more than one TE much in any case, so why bother activating a TE.