Why do some violin scale books, after starting with C Major and A minor, then work through key signatures up to six flats and then work down from six sharps?
That sequence follows the Circle of Fifths, which is very typical of root movement for chords. This also follows a path of minimal alterations from one scale to the next.
Here are some example chord progressions.
A ii - V - I progression in C would be Dm7 - G7 - C, and in D♭ this progression would be E♭m7 - A♭7 - D♭. If you look at the Circle of Fifths you will notice that the root notes of the chords follow the Circle in both cases.
Another common progression that follows the Circle of Fifths is iii - vi - ii - V - I. This progression obviously contains a ii - V - I, with a couple of chords preceding. In C this would be Em7 - Am7 - Dm7 - G7 - C.
But not only do chords often move in this way, keys also often modulate around the Circle of Fifths. Since adjacent keys on the Circle differ only in one note, they are closely related. For example, C has no sharps or flats, but F has one flat (B♭), and G has one sharp (F♯), B♭ has two flats (B♭ and E♭), and D has two sharps (F♯ and C♯), and so on.
Since it is common for chord roots and keys to follow the Circle of Fifths, it is useful to study scales organized in this sequence. It may also help memorization to have this pattern in your mind.