The game used to be played in the middle of the afternoon but the networks figured they could get more viewers with the game being played at night.
The nets also use it to trot out some show that they want to draw a big audience to. If it's not a new show, it's always one of their bulwarks that they want to highlight. I remember a 1 hour "Friends" a few years ago with Jean-Claude van Damme after one of them, but usually, I've switched to either the History Channel, ESPN, or Fox News once the game is over.