Some other reasons why musical notation prevails:
- There's a huge switching cost, as much of the world's written music is in some form of "western notation". Being able to read standard notation unlocks a huge wealth of knowelege from books, etc.
- Standard notation is one of the most flexible ways to create readable music, playable and easy to read across a wide variety of instruments and ranges (clefs, transposing score, etc).
- It's a common language, in the way that a programming language is. Some of the conventions may be confusing to outsides (i.e. why is the term "puts" used for printing in ruby? this seems normal to any ruby hacker but is completely unintuitive to a layperson). Once these conventions are learned, they provide common reference point. Like a lot of languages, it's far from perfect, but much like spoken language, more likely to evolve than be replaced.
- There's almost no motivation for anyone to replace standard notation. Notation isn't required for all forms of music (many great jazz and blues musicians don't read music), and for the forms of music where it is required, it's by far the quickest and most efficient way to communicate the information.
In summary, I think the question of "why can't we do better" is valid, but you could ask the same question about programming in C. There are good reasons to write C in 2017, and there are still good reasons to write musical notation.
It's definitely true that most jazz musicians can read passably, but my original point was that it's an aural tradition. no one learns to play jazz reading notes off a page. Whereas in western classical music, it's an essential skill.
https://www.amazon.com/Erroll-Garner-One-Hear-Read/dp/B00AZ4...
Before starting down that path, I would recommend familiarizing yourself with the wide range of music notations that already exist and continue to be used, and then the ridiculously varying plethora of failed alternative music notations that have been invented over the centuries, and why they failed to see wider adoption.
And, of course, it's fascinating to study the evolution of the existing "standard" music notation, and see the changes that have been adopted, and the ones that weren't. For all its apparent stasis, it has definitely evolved over the centuries, in response to the changing needs of musicians.