Sun rays walls directly onto areas that are on the equator, whilst they get more slanted nearer the poles. so if you can imagine it the sun rays at 90° or perpendicular to the earth at the equator, due to the curvature in the earth, they 'tilt' in a way when you get nearer to North/ south poles. Therefore it is the Latitudinal Extent (how far one goes towards a pole/ away from the equator) that influences the chance of different durations of day and night.