This started out as a super easy song for beginners, only three chords. And I start teaching it in C major, which is even easier. Later I add a Db major chord.
But this version adds a modulation, then the last page adds octaves and a full chord at the end. Then a C7 and G7 is added to make the modulation smoother.
Is it still really easy? To be honest, no, it’s not. It just sounds a lot better.