But "music hall songs, swing, boogie-woogie, ragtime and [to a certain extent] rock and roll" are now regarded as "historical" musics and have been displaced.

I also don't buy this argument that the music that I like must also be relevant to 'ordinary people'. How relevant were swing, boogie-woogie and ragtime relevant to 'ordinary' British people in the past and how relevant is rap music relevant to 'ordinary' British people today? I would suggest that they were or are relevant because they were or are fashionable. Personally, I've never 'got' fashion (but surely the Emperor is naked?!) and it doesn't influence my tastes.