Key signatures and accidentals have a practical benefit in indicating the tonal centre. All pitches are not equal, at least not at any given moment. Sharps and flats look like a kludgy hack, but they provide clear visual hints of highly relevant musical information.

There are alternatives to just having a huge number of lines. Western music notation already has one: the grand staff has a gap in the middle. Simply put a gap with a single ledger line between each octave and you get a system that looks an awful lot like the current system. It's like spreading two octaves over a grand staff, but with a more modest gap in the middle.

So you can still have sight-reading. You also get fully arbitrary sight-transposition, which today is only possible for the very most elite musicians.

> Western music notation already has one: the grand staff has a gap in the middle. Simply put a gap with a single ledger line between each octave and you get a system that looks an awful lot like the current system.

Except that's not how a multi-staff partition works. Each staff has a clef that determines it's offset; they can be the same or wildly different. They also usually signify different "voices" or instruments, further encoding musical nuance beyond pitch and tone.

But you want each key to look different because physical instruments are all tied to a key. If every transposition looks the same then you've just turned a visual transposition problem into a physical transposition problem.

Physical instruments aren't really tied to a key.

Transposing instruments only even exist because sight-transposing is so difficult. There is nothing fundamental about an instrument that makes it transposing. We only use that kludge because of the difficulty sight-transposing.

Suppose you do have a transposing instrument though. It's in Bb, and you'd like to play music written for an instrument in F. Very few musicians can do that without hesitation.

The same applies when there is a desire to shift the entire piece of music up or down. Perhaps you are using a hecklephone instead of a lupophone, so you shift everything up. Perhaps you just lost a trumpet player with an unusually high range, and thus need to shift everything down. It would be great to be able to expect all players of ordinary skill to be able to do this without hesitation.

BTW, I'm aware that one needs to avoid troublesome notes and things like impossible trombone glissandos. This doesn't change the general truth of the above.

You say it doesn't work but it's been used in a variety of ways such as singing video games (eg. SingStar) and music trackers [1], and it works just fine.

[1] https://en.wikipedia.org/wiki/Music_tracker

Working in a game where mistakes don't really matter and working for professional music production where mistakes and restarts cost $$$$$$$ are nowhere close to being the same thing.