Even today, most musicians learn music by an aural tradition. They hear it, they learn it. Music notation developed as a way to transmit works of music across time and location. It has its uses, it has its limitations. Here are some links to get you started towards understanding the evolution of musical notation.
Good Starting Article, with Many Examples
Another Good Overview (some humor too)
Could Music Notation Develop Further?
Does Music Notation Matter for Electronic Music?
https://www.youtube.com/watch?v=NOuHKlpkOmE