Asked to me on Quora
Because it’s the first scale everyone learns. 😉
And scales aren’t easy to play.
But C Major will become the foundation you build all of your coordination on.
And soon you’ll soon be able to play in new keys – F Major, Bb Major all the way up to Gb/F# Major.
And as your scale practice increases your confidence and poise, your fingers will start to move on auto pilot, easier and faster.
And by the time you return to C Major – that smooth landscape of no sharps or flats – your fingers will just fly.
So I guess the beauty and irony of C Major is that it is both technically the hardest scale to learn, but the easiest scale to play.