The FAA sent us a bit more detail about why it's banning drones at Sunday's Super Bowl. As you may have predicted, the ban stems from legislation passed after 9/11.
An FAA spokesperson explained in an email:
The flight restrictions over major sporting events were imposed by Congress in legislation passed after the 9/11 attacks. The FAA's Superbowl [Temporary Flight Restriction] implements that mandate. There are also federal rules passed after 9/11 that prohibit unmanned aircraft and model aircraft in Washington, DC.
This makes sense, but those laws hold the same relevance in 2015 as they did in 2001. A decade and a half ago, drones didn't exist in the way that they do now. In other words, those laws didn't anticipate a near future where a few hundred dollars could buy an aircraft that anybody could easily fly. (It's also worth remembering that some of the post-9/11 laws around flight restrictions are absurd in other ways, like the Disney no-fly zone that's really about keeping advertising away from Mickey Mouse's lair.)
All that said, the absurdity of the FAA's Super Bowl drone ban has less to do with enforcing post-9/11 legislation and more to do with the lack of new, drone-specific regulations. In a sense, the existence of cheap, easy-to-fly drones means that major sporting events are even more dangerous today. So nobody is disagreeing with the FAA trying to keep everybody safe. That's a valiant and essential mission. But maybe let's hurry up on those drone regulations. This is getting absurd.