If we take out the consideration of the Captain being locked out and the various Facebook theories, what are the possibilities of the PF having a mini-stroke or other cognitive impairment? Was he confused as to the stage of flight and fixated on the landing briefing in a state of semi-consciousness thinking that he was to commence descent?
Even for someone that is deranged and about to kill himself and all his passengers and crew, it would be surprising to me that he did not say a word (or so it appears).