Why is there music in pi?

This is actually one of many interpretations of Pi; and even then, from a music theory point of view, it's, technically, "bad" music.

First off, the choice of mapping Pi on a major scale is a huge step in "forcing" it to sound good. Because most notes of the major scale sound good relative to one another, then playing random note on a major scale would still give "melodious" results.

However if you were to perhaps map Pi on the chromatic scale, or even on some tuning directly based off Pi (example: 1 = 100Hz, 2 = 200Hz, and so on), then i doubt the result would be as melodious.

Additionally, from a structure point of view, the song has a very bad structure. There is no motif, for instance. A motif is a group of notes that repeat once in a while to provide the basis for the song. In fact, the major scale interpretation of Pi is good, as a song structure, only to the extent that it happens to randomly hit unresolved notes once in a while, which causes tension and therefore unexpected (but welcomed) interest.

What a good question though. I haven't heard any interpretation of Pi before - and I do concede it actually is somewhat beautiful, at least in the major scale!