What if you're in an exit row, last to board and notice an open seat in F and no seats in Y? You say that you don't feel like you're fit for the duties of the exit row. They have to move you to another seat, and it'll be quicker for them to move you to the open F seat than look through the Y list and pick out a passenger deserving of an upgrade, move all their stuff to the F seat, and then move your stuff to that Y seat.