I'm not sure the Nobel Prize has to do with who writes the best songs or books. Here's a quote from Alfred Nobel according to Wikipedia: "in the field of literature the most outstanding work in an ideal direction".
There's some discussion of the meaning of "ideal direction". It seems that early on that was taken to refer to idealism but in recent decades it's become more liberal so that it can mean either idealistic or having literary merit.
It's worth reading the article about this:
https://en.wikipedia.org/wiki/Nobel_Prize_in_Literature
Barry