The last of the great rockers are all in their 70s. Have a conversation with many in their 20's about these groups and you'll usually get blank stares or maybe a comment about how their dad had their cd. Reality.
The halftime show is now firmly more a "show" than it is a mini concert. Dancers, props, fake guitar playing, pre-recorded tracks, etc. It's visual. It's diverse across genre. It's safe. It's the NFL. Presumably it's profitable.