John Nesbitt narrated quite a few shorts back in the 1940s...all with a strong nostalgic bent. While he had a pleasant voice, often I disliked the films because they never allowed the actors in it to actually talk on screen...and having Nesbitt describing everything really reduces the film's impact...making it seem disconnected and dull.
In "That's Why I Left You", a husband dumps his wife and leaves a note explaining why. In it, it recounts their happier days. Ultimately, however, he was a selfish jerk and left because of his sense of wonderlust. What a jerk...or so it seems
So, you have a relatively uninvolving story and dull narration. Nothing special here.