Irrespective of medium, representationality, or message, art to me is about an act of creation. And I don't mean this in a religious sense.
Creation is about ownership. It's about bringing something into being that is yours. With pure art it's about bringing something into being that is non-functional, though a gray zone exists with architecture, furniture-making, and even disciplines of entertainment.
When at least an element of your creation is non-functional, you have made that creative choice for aesthetic (or perhaps philosophical or narrative) reasons that don't require function, or efficiency, or economy.
To me there is an impulse in many of us to be creative. And whether the fruits of our creativity are representational or not doesn't matter so much -- they all stem from the same drive.
Incidentally, I've done some reading about musical aesthetics, and as I understand it most music really does not have much resemblance to naturally occurring sounds. Bird songs are atonal, for instance. Pieces of classical music that evoke nature (Beethoven's Pastorale, Vivaldi's Four Seasons, Stravinsky's Rite of Spring, etc) don't really sound much like actual nature. I suppose the second movement of Mahler's 7th Symphony sounds a bit like bird songs, but in a very stylized way.
One exception to this is the African tama (the talking drum), which to an amazing degree mimics the inflections of the tonal languages (esp. in Nigeria).