Why is it that when our cognitive systems engage in visual and auditory information-processing, we have visual or auditory experience: the quality of deep blue, the sensation of middle C? How can we explain why there is something it is like to entertain a mental image, or to experience an emotion? It is widely agreed that experience arises from a physical basis, but we have no good explanation of why and how it so arises. Why should physical processing give rise to a rich inner life at all? (David Chalmer, Hard Problem of Consciousness).
I have always thought that too much interest in why certain things happen leads only to frustration (which occasionally produces a book or two, and maybe tenure for the really lucky among us, but at what cost to the soul?). The prime objective of a beautiful life, to my mind, has never been to take all our aesthetic relationships and reduce them universally to one rational narrative (however elegant); the best theory of art (say that of Schopenhauer), lovely as it is, pales in comparison to art itself (especially when one discovers some art that one really loves doing).
I do not say this as someone who hates theory. On the contrary, I love it (and Schopenhauer’s theory of art) a great deal, akin to the way some people love painting or music. But it is only partial, a single piece in a puzzle too large to be finished (or fit together too neatly). To focus too hard upon finishing the puzzle once and for all is to neglect other things: Schopenhauer himself made time to enjoy art, not just to reflect on it, and I am not persuaded that he wouldn’t have done better to practice it more (to get out and make something, even something ‘inferior’ to the greatest of which his generation was capable).
I don’t think there is such a thing possible as a universally satisfying explanation for art. (But if that is what you are looking for, you could do worse than to read Schopenhauer.)