To paraphrase someone (who does not exist on FR and who has never existed on FR), things are wonderful and beautiful in the same way that jello takes the shape of the jello mould. It really shouldn't be surprising that we find some things beautiful and others ugly. A different sentient species would find different things beautiful. (He who does not exist on FR and who never existed on FR put it better than me.)
How about this: Why are some things tasty and other things taste bad? Why is the urge to sneeze such a compelling urge? Why is sex so pleasurable? Beauty is a much more subtle phenomenon than deliciousness or sex, of course, but there's no reason to believe "beauty" is some kind of supernatural floating abstraction or something.
Well, this is pretty simple. Evolutionists would point out that some things are tasty to us and other things taste bad, because natural selection gave us defenses (imperfect ones) over time from eating poisonous or harmful plants. We have the urge to sneeze, they would say, as we developed through natural selection a means (necessary for survival) of ejecting foreign substances from our nasal passages. Sex is so pleasurable, because otherwise we wouldn't propagate our species. But I fear you missed the point. It is much, much harder to show, from a natural selection and survival of the fittest approach, that a species would be expected to develop such an elaborate system of sounds (music) and means to produce them - or that a species would devote so much of its time and energy to that pursuit. Music, as an example, does not fit well (or so it seems to many, including me) into evolutionary theory.