It's actually trademark rather than copyright law that's in effect, with the argument being essentially about money (although there are some other considerations in the mix, too.)
It was back in 2004 that the NFL clamped down on what it called unauthorized commercial use of its trademarked terms "NFL," "Super Bowl," and "Super Sunday" and it's been vigilant in its protection of the brands ever since (to the extent of hiring undercover agents to seek out unauthorized parties at Las Vegas casinos). As a result, many events and promotions tied to the Super Bowl, but not sanctioned by the NFL, are now forced to refer to the event with euphemisms such as "The Big Game."
Not only are commercial entities like casinos or bar venues not supposed to profit commercially from its showing; screenings are also prohibited in churches or at other events that "promote a message," while venues that do not regularly show sporting events cannot show the Big Game on any television screen larger than 55 inches (hence the disappearance of the famed Las Vegas casino parties that used to take place in ballrooms and meeting spaces that don't usually feature sports broadcasts).
Following its successful 2004 move to win back control of the Super Bowl and its associated trademarks, two years later the governing body attempted a wider sweep, with an effort to trademark "The Big Game." However, enough was enough, and the NFL subsequently withdrew the application in 2007 due to mounting commercial and public-relations opposition. Much of this came from Stanford University and the University of California, Berkeley, and their fans, as the Stanford Cardinals and California Golden Bears football teams have been competing annually in their own Big Game since 1892, decades before either the Super Bowl or the NFL even existed.
