I think the premise of this thread is flawed and a victim of the blinders of relative cultural and age perspective. I mean, by the OP premise, music has been in decline since Bach stopped writing music.
Idk. Saying contemporary pop is in serious decline...based on what? Musical structure superficiality? Compression? Whatever. People were saying the same schitt in the 80's and just about every decade.
We we grow older. Music changes and doesn't fit into our established impression of what defines good music, and thus we dismiss it or grudgingly accept it if it's close enough to some schema we recognize.