A Bunch of Pieces in Treble Clef

Czerny and other romantic composers of numerous easier teaching pieces for piano often set both hands in treble clef using easy keys, especially C. I decided to follow suit, but my collection is a bit different: each piece has a separate title indicating the mood or main idea; I use keys with lots of flats and sharps; and I sometimes use asymmetrical meters and unusual phrase lengths (5 or 6 bars). Why does everything have to be in four-bar phrases?