It’s not about the sound, it’s about the mechanics of performance. On an alto sax, ‘A’ is 370Hz On a tenor sax, ‘A’ 237Hz But in both cases it’s the note you

It’s not about the sound, it’s about the mechanics of performance. On an alto sax, ‘A’ is 370Hz On a tenor sax, ‘A’ 237Hz But in both cases it’s the note you get when you close only the 2nd hole. Because of the transposing convention, if you take someone who can sight read, but is familiar only with the alto sax, and hand them a baritone sax and baritone sax sheet music... they’ll basically be fine. If all saxophone sheet music encoded A=440hz, they’d have to relearn which note on paper corresponds to which set of buttons. That said, the relationship between the instruments in a family is important, but the specific keys are a historical accident. In woodwinds specifically, the instruments that ‘won’ and remain common are mostly b-flat, with e-flat in second place. If we could take all existing woodwind sheet music and shift the notes up 3 semitones, we’d instead have ‘c’ and ‘g’ woodwinds, where ‘c’ meant it matches non-transposing instruments. We could start doing that now, but no-one’s really interested in making a breaking change.