The underlying assumption here seems to be that white people don't listen to hip-hop, which I don't think is true at all. I think Superbowl audiences just span several generations and Kendrick, while pretty popular, isn't so famous to be known by a lot of old people. This has been an issue with Superbowl acts for a while now... there's not as much of a monoculture with pop music as there used to be, and so musicians aren't reaching the same status in pop culture as they used to.