It’s because it wouldnt help for sight reading the way you might think. Especially where there’s multiple voices like in complex piano parts. For example if you want one note to for 8 eighth notes in 4/4, but some to go for 10. Now we have to choose to use current notation or the new fangled “whole measure” or even “rest of measure” notation, and if using new fangled, we still use old notation for edge cases.
It’s because it wouldnt help for sight reading the way you might think. Especially where there’s multiple voices like in complex piano parts. For example if you want one note to for 8 eighth notes in 4/4, but some to go for 10. Now we have to choose to use current notation or the new fangled “whole measure” or even “rest of measure” notation, and if using new fangled, we still use old notation for edge cases.
It’s hard to fight the status quo.