I imagine it's less about "rock music" and more about the disappearance of "bands" from the mainstream. Almost every charting artist now is solo and makes pop music, which greatly limits the variety available to listeners, and encourages labels to push copycat acts because they feel those are the only ones worth taking a risk on. The Oasis reunion is an example of this: they are a band selling out arenas and pocketing millions performing songs from the previous century, and facing little in the way of competition because bands like them are largely extinct.