It's because the central time zone stations get their feed from the "east cost feed" - I BELIEVE the Mountain Time zone stations MOSTLY grab the West Coast Feed
Interestingly, the West coast feed IS 3 hours behind the East Coast feed for 90+% of the shows (Obviously live is not etc)
I know, for instance, Good Morning America (I used to work for ABC) is done live on the East Cost, and is taped for the west cost feed, UNLESS there is something 'breaking', and then MOST of the show is still 'in the can' and they keep the studio hot to do updates in the news segments. Used to cause all sorts of havoc with me scheduling in computer/software updates, because computer support down there usually left for the day around Noon-1:00 (or earlier) as they basically worked mixed shifts that started as early as around 10:00pm the night before. Most folks start at 2:00am, so when the show is going off the air at 10:00am eastern, they have done their 8 hours, and just want to go home
Some good folks down on the crew over there. For tech geeks, I think watching the control room is a LOT more fun than the show itself. Eaxactly how they handle any breaking stories, how they decide what IS breaking, and how they handle when a guest goes over their time slot by30 secons, or worse, 2-3 minutes - remember, they STILL have to make the commercial breaks on the EXACT second