Thanks for this comment, it is well thought out. Many composers actually composed using themes from forgotten folk music in regions around them. For example, Béla Bartók's Mikrokosmos uses themes from folk music. Bartók uses scales, and forgotten themes from folk music in this. Another classic example is Percy Grainger's Lincolnshire Posy. We played Lincolnshire Posy this year in wind ensemble. It was a lot of fun to view how Grainger incorporates themes that had never been written down, and in most cases only sung for centuries (passed down orally). It has a lot of weird time signatures as a result, but it is quite beautiful (especially the second movement).

You are right that almost every genre uses the same foundations, I feel that classical music has a much more strict definition of how each of the principles is to be used, while other genres, Jazz for instance, have looser rules that allow composers to almost always go out of the box. I guess it's a question of musical taste.
Thanks for commenting! I followed back.