@FH2104 It's too depressing for a Christmas special! The vast majority of it is the entire human race being hopeless and scared, with things only starting to get better when the Doctor finally wakes up.
And people say EastEnders is all doom and gloom at Christmas. (Ironically, Christmas 2005 was a relatively happy one for the soap. It's like Doctor Who saw what EastEnders where doing for Christmas that year and decided they needed to fill the depressing Christmas Day TV-shaped hole in the schedule)