Yeah, that drives me nuts too. Or used to until Sunday Ticket came out.
On the surface, because of the concentration of teams in the East/Midwest, though it'd be easy enough to make the SD/KC and NE/HOU games late. I suspect the real reason is in the TV deal, forcing the whole country to watch the national Fox DAL/GB as the only choice unless you're in Oakland or Devner. They probably pay the league a premium for a few of those a year.
On the surface, because of the concentration of teams in the East/Midwest, though it'd be easy enough to make the SD/KC and NE/HOU games late. I suspect the real reason is in the TV deal, forcing the whole country to watch the national Fox DAL/GB as the only choice unless you're in Oakland or Devner. They probably pay the league a premium for a few of those a year.