Because it is not about football during halftime...it is not even about those at the stadium...it is about making the tv audience grow, beyond those who watch the game.
Yup - but if it's truly about expanding the TV audience they need to be more creative and cross multiple and diverse genres. As an example, why not have a popular country artist thrown in as well if it's really about mass appeal. I'm not the biggest country music fan but it's probably one of, if not the most popular genre in North America and quite so in other parts of the word too.