Kiss had a duet with Adam Lambert in American Idol. Adam Lambert a “rock god” as per Kara Dioguardi performed a rock song live with none other than KISS.
I think they’re showcasing what the inner talent, inner artist of the finalist are. In this case, Adam is a “rocker” and it is just fitting to have a famous rock band to go on stage with him.
I wished it was Axl Rose and Adam Lambert singing Sweet Child of Mine. That would be awesome. I find KISS to be on the “wild” side of rock. Too wild for my taste.