Music notation is a mess.
I'm not proposing changing it (that would make no sense -- it's good enough), but it's not worth treating as somehow right. Centuries of unplanned historical evolution don't necessarily result in something rational.
To go with your analogy: it's like the legacy software system written in Fortran which runs on VMS. There's a ton of institutional knowledge and good ideas, but a ton of cruft too.
In that sense it's much more forgiving than software. Software becomes indecipherable almost as soon as nobody is looking at it and its structures are in some sense necessary for a purpose. It's not as amenable to pragmatic solutions although often, more of them are possible than we recognize.
A lot of the notation of timing is cumbersome. Why the large number of wonky-looking symbols? Compare to how a lot of composition software shows timing with how long a position notes take up horizontally (music notation predates the concept of Cartesian coordinates!). It's a lot easier to work with, in all respects.
All this stuff builds up to about an unnecessary 3-month learning curve for kids learning music notation.
Is it worth changing a whole industry -- where everyone already knows the notation and there are countless works in notation -- to save all kids three months? Maybe, but probably not. That's the legacy system problem.
The nice thing -- compared to software systems -- is that none of this stuff is really all that complex.
Why do you say so?
>literally every other context ever in the history of everything
Have you met a single non-programmer that counts in everyday life starting on 0? Do you even start counting with your fingers from 0?
I'm not sure about the target audience. For example, I looked at the Pitch poster (notation-pitch.pdf), and it seems to target people starting out on the piano. Nothing wrong with that, but people starting on instruments that don't have pre-programmed pitches (violin, cello, trombone, ...) Probably want to know there's a difference between fi c-sharp and d-flat.
Also, there's a cultural divide in how you read notes (movable-do versus fixed-do) and I'm not sure what you want to do with that.
Music theory is a mess.