There are people who look at the rules and find ways to structure around them. The more complex the rules, the more opportunities.
But when you get to a song, not only do you have to do a vocal melody, you have to write words and not be redundant and make some semblance of a story.
I believe that the brain has evolved over millions of years to be responsive to different kinds of content in the world. Language content, musical content, spatial content, numerical content, etc.

