Why are there no NFL games on Saturday December 8?

I've always wondered why there are no NFL games on the Saturday after the College Football Conference Championship games. It seems like a perfect day to have a prime time game (or two). Without any football today, it doesn't seem like a Saturday at all. (I'm sorry, but the Division I-AA playoff semifinals doesn't do much for me). I'd imagine the NFL has looked into it since they clearly know how to make money. So I wonder what their reason is for not having a game or two today.