For the same reason we don't teach everyone the Greek alphabet -- because they're not really going to use it unless they're going to be reading Greek?
For the same reason we don't teach everyone the Greek alphabet -- because they're not really going to use it unless they're going to be reading Greek?
And it fact it seems we try to teach kids music notation - at least I had group recorder lessons in elementary school, and I thought this was pretty common?
But we fail. On each step in my school career from elementary to high school, they assumed we hadn't learned anything in the previous level. Which was, for most people, true.
A few, including me, learned to read traditional music notation well enough to play recorder pieces we weren't supposed to. But it didn't help me - or anyone I know - to be able to sight sing, for instance. It wasn't possible to build on for anything, except maybe becoming a better recorder player.
Having a "simplified musical notation system" might enable many more casual people to be able to sight-sing. But how useful is that, practically speaking? After all, you can just ask your musician friend to play through the melody a few times and then you know it well enough that the full musical notation system can remind you.
In fact, one simple option would be to teach people basic music theory based on C being the root, then write the vocal parts transposed into C and on a C clef. No need for super fancy new notation.
But such a system would have the opposite issue if anyone wanted to play it on a real instrument -- then they'd need to have enough musical theory to be able to transpose whatever they were looking at into the specific key they were supposed to be playing.
Furthermore, if you're looking at music, you're almost certainly going to be playing with an instrument anyway; in which case, you ideally want to practice in the same key the instrument is going to be in. In which case, it's probably better to just teach singers enough piano to be able to plunk out the tune on the piano when practicing privately until they "get" it.
On the whole, it's not clear that any possible improvements to the current system of "Have the people who can't sight-sing listen to the instrument until they get the idea" will be worth the extra costs.
That's just solfège (Do-Re-Mi) and kids do learn it traditionally. Translating from sheet music to solfège is trivial once you know the piece's key, since both are based on the diatonic scale.
We've had alternative systems for more than 150 years, and they have been undeniable didactic successes. So-called "moveable do" systems incorporate the "music theory framework" as you call it. But conservatories are refusing to build on it, all these things get accepted only as stepping stones to "real" music notation, not as something potentially transformative.
The arguments you make could easily have been made against the teaching of regular literacy too, once: it would certainly not have been obvious before the fact what the fruits of "everyone mastering this" would be.
Chinese notation is also moveable do. So is Roverud's cipher notation which I mentioned above (I think it has a common root with the Chinese one). So is the Kodály method. All these systems have been really successful in teaching where they were applied, but they always fall for the push to graduate to the "real" notation system.
I took many more music classes than required and sing/read hymns regularly and I feel fairly musically literate. It just needs regular practice like anything else, especially singing. Another thing to keep in mind is that musical literacy is of limited practical use and most people get by with performing by ear just fine.
I remember asking my mother how she could sight sing so easily (she got her degree in music). She told me you have to practice it intentionally like you practice playing your instrument. It's always difficult at first. Blew my mind. I was hoping there was a lazy way to learn, so I would just automatically become a sight singer from practicing my instrument, but alas, no.