The easy answer is that the piano is not the "reference" instrument. If you look at a violin, the A major scale is generally the first scale you learn -- not C.
The piano has C natural in the middle of a full 88 keyboard, which is why it is a "natural" scale to pick (C major only uses the white keys, while A major would use three black keys).
So if you are learning another instrument, your "base" note will sometimes be entirely different.
Many "non-western" tradition also aren't tuned to 440 Hz, and even many _western_ traditions don't use 440 Hz for A, 415 Hz is also common.
[addendum]
And why Do/Ut, Re, Mi? Because of a Gregorian chant where each sound sorta fell into a vocal range of monks ... then you adopt Do to whatever "sound" the instrument is closest, many years pass and deviations and standardizations ...
[addendum]
I recommend starting out researching Guido d'Arezzo (and the Guidonian hand) a bit, that is where we get do/re/mi .. which was used as a teaching aid (which is maybe why Solfege as a term is often used in combination to sight reading or singing from sheet music). Almost no matter what language someone sings/voices Do/Re/Mi/... ... it falls naturally into a vocal range, irrespective of octave.
And then one could look into the hexachord ... and deep into a very deep well of confusion.
> The easy answer is that the piano is not the "reference" instrument.
The question make sense without ever thinking about piano. The question is: how come the notes named only by letters (without any accidentals) form a major scale, and yet the note A is not the first note (or tonic) of that scale.
The answer is probably related to the fact that those notes also form other scales (seven of them - seven diatonic modes, one of which corresponds to major scale), and it's only relatively recently that the major scale took a central role in music theory.
You will need to blame Boethius, musical notation is a quagmire of many systems that have been merged over centuries. If you venture into non-western systems, it becomes even more fascinating.
Maybe we should make one more standard .. that consolidates all of them? ;-)
The piano has C natural in the middle of a full 88 keyboard, which is why it is a "natural" scale to pick (C major only uses the white keys, while A major would use three black keys).
So if you are learning another instrument, your "base" note will sometimes be entirely different.
Many "non-western" tradition also aren't tuned to 440 Hz, and even many _western_ traditions don't use 440 Hz for A, 415 Hz is also common.
[addendum] And why Do/Ut, Re, Mi? Because of a Gregorian chant where each sound sorta fell into a vocal range of monks ... then you adopt Do to whatever "sound" the instrument is closest, many years pass and deviations and standardizations ...
[addendum] I recommend starting out researching Guido d'Arezzo (and the Guidonian hand) a bit, that is where we get do/re/mi .. which was used as a teaching aid (which is maybe why Solfege as a term is often used in combination to sight reading or singing from sheet music). Almost no matter what language someone sings/voices Do/Re/Mi/... ... it falls naturally into a vocal range, irrespective of octave.
And then one could look into the hexachord ... and deep into a very deep well of confusion.