Some of the greatest music ever written was "absolute music", meaning that it did not reference anything outside of itself, lyrically or thematically. Someday there will be a return to this form and the blaze of brilliance created by its innovators will cause all of this human-focused music to pale and wither.
A few questions to ponder:
Did not the nineteenth century already have much to say about this notion of "art for art's sake"
? Wasn't this period the triumph of humanism?
Isn't the practice of self-reference in art, by definition, a kind of egotism? How could it possibly not be human-focused?
You may find a worthy challenge, and answer, in Richard Weaver's chapter "Egotism in Work and Art" in his book Ideas Have Consequences
. (I can only provide you a link to a fragment of this chapter.)