Super bowl advertisements cost millions of dollars for a few minutes time. The design/goal behind super bowl ads is simple, get people to buy stuff. That is what a majority of the advertisements are for the super bowl. The ads definitely cater to a certain populace and the stupidity of the commercials often reflect this.
If a company is willing to pay millions of dollars for a coveted few minutes of advertisement time during the super bowl their message had better be clear. In recent years the commercials have been dumbed down almost to a degree of complete absurdity. The funnier the commercial, the more memorable the message. This constitutes successful design in advertising.
Contests for 30 second spots during the super bowl spur very interesting designs. Fans can create commercials and if their idea gets selected it can be aired during the super bowl. This creates fresh ideas and memorable ads. There are also awards for best super bowl commercial as well.
The NFL and most professional sports in general are cash cows. The money from advertisements fuels the player salaries and helps stadium construction efforts.