Why do people try to argue that certain music is no longer "relevant"?

I notice a lot of professional and amateur music critics will often try to belittle certain artists/bands and genres/subgenres of music, arguing that they are no longer "relevant" or something along those lines. But as long as music is recorded and available for anyone to listen to, how can it not be relevant? You never know who might pick something up and get inspired by it. It just seems like a weak attempt to make someone's taste seem superior and everyone else's seem inferior. And who's to say that mainstream success/exposure equals relevance? Mainstream success is a very fickle thing.