Because art belongs to society. Revenue belongs to individuals.
Exact works of music that should be public domain. Ehhh, fine. Unless it's a cover. In which case it's new art.
Art doesn't belong to the artist.
So, if I paint a really nice picture that I hang on my wall, when I die you think that my son should not inherit it? That it should "belong to society"? So, whoever wants it should come and get it, for free, like? No? That would be stealing, wouldn't it? Or that it should automatically be transferred to a museum for all to see? To me that sounds awfully lot like communism.
My son can sell it, for money, if he so decides, or keep it away from "society" forever, if it's his choosing.
Why should it be any different for music? Why shouldn't anyone be allowed to inherit music, or more specific rights to?
Painters can let relatives inherit his or hers painting and sell for profit. Why shouldn't composer be allowed to do the same?
You see, it's a lot easier to get "the same experience" from a copy of a recording than from a copy of a painting. If you've ever visited an art museum, you know what I'm talking about. So, paintings/art sell for obscene amounts of money since people want "the real experience" (and of course the possible rise in value), but for composers it's not the same thing, they need the very tiny revenue to trickle in to make their "fortune" out of their hard work.
I can tell you that if your idea ever got traction, "14 years of copyright", there would be no radio stations playing anything newer than 14 years ago, and the music industry would instantly come to a grinding halt as noone would ever write a song again, since you can't make a living out of it.