And Led Zeppelin’s success is far more than a sum of its parts. Part of it is nostalgia among those who heard them in high school and hold that moment.
Robert Plant solo doesn’t have the same draw or appeal and Jimmy Page doesn’t want to do the reunion circuit.
Part of nostalgia is nostalgia, but part is hearing loss. It's harder to appreciate new music when we can't hear the higher frequencies any more. We remember what the songs of our youth sounded like, including the higher frequencies, and our minds fill the missing parts in for us.