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.