There are many ways in which the Super Bowl halftime show is quite different from an ordinary concert: It’s once a year, it’s wedged in the middle of the most-watched sports event in America, and the NFL picks who gets to perform. Another key difference is that, whether the audience knows it or not, the halftime performer doesn’t get paid.

“I'm sure they want to be compensated, but in terms of events here in America, the Super Bowl halftime show is one of the best for an artist from a branding perspective,” says Derek Rucker, a professor of marketing at Northwestern’s Kellogg School of Management who evaluates brands’ presentations of themselves every year for the Kellogg Super Bowl Ad Review. From the huge audience—viewership each year regularly clears 110 million—to the media coverage both before and after the Super Bowl, he says, there are major benefits for a performer.

The benefits are considered so major, in fact, that, as The Wall Street Journal reported in 2014, the league has asked some artists to consider paying for the privilege of performing at halftime. It was speculated that this detail was leaked as a negotiating move by an artist looking to make a deal with the league that year, and the hope was that the musicians would win over the public on the idea that performers shouldn’t have to pay to take the stage. In the end, no one paid to perform that year.

In the years since, musicians have made a point of saying that they didn’t pay to play. Last year, the singer Katy Perry told the Associated Press that she “put [her] foot down very early” in her negotiation with the league. And on the same day the announcement was made that Lady Gaga would perform at this year’s Super Bowl halftime show, ESPN reported that both the NFL and Pepsi (which sponsors the halftime show) made official statements that Lady Gaga did not pay the league, nor did they pay her.

Why has it become a ritual for both sides to come out saying that no money has changed hands? Rucker sees it as a protective measure for both sides: For the league and the artist, the faster the compensation conversation is over with, the better, because both parties would rather have people remember a great show than a contentious financial battle. “I think it has to do with authenticity … It's almost like these technical details risk ruining the experience,” says Rucker. “In certain categories, the how matters. You look at organic foods, and there's a huge pitch in how it happened. In this particular case, that conversation detracts from the event itself.” Additionally, the performers and the league’s statements are partly to defend their respective worth: A halftime show is a truce between an extremely high-value artist (as Zack O’Malley Greenburg notes over at Forbes, these performers are capable of making millions a night) and a highly coveted performance spot.

The NFL, for its part, has always claimed that the math works out for performers. The halftime show is an honor that carries with it tremendous exposure. Plus, the NFL fronts the production costs—reportedly upwards of $10 million for Lady Gaga’s performance this year. My colleague Joe Pinsker once pondered the question of whether performing in the halftime show is worth it for the musicians, and concluded that though it’s a hard-to-quantify value proposition, the upsides of the exposure and the acclaim of performing in the show likely win out. In other words: The Super Bowl halftime show is basically a one-of-a-kind, ultra-prestigious unpaid internship.

It’s possible, though, that that calculus might change in the coming years. Concerts have become a bright spot for the music industry as losses have mounted thanks to plunging physical and digital sales; the value of live concerts has been going up, in terms of gross revenue as well as tickets sold. Concert tickets have been getting so expensive that the former White House economist Alan Krueger, who reviewed the data in a lecture called “Rockonomics: Economics and Public Policy in the Rock and Roll Industry,” found that the most-popular performers were the ones most likely to capture gains from these increased ticket sales. That means that the exact same artists who are likely to play the halftime show are becoming more and more valuable as live performers. Meanwhile, the NFL’s ratings fell in 2016, leaving people to wonder whether it has peaked as a cultural symbol. If the NFL’s prestige declines and live performances continue to climb in value, the winning proposition might one day not be one in which no money changes hands.