Maybe it is because darkness makes the engine more prone to failing????
Haven't you ever seen Gremlins???
I've done night flying towards my PPL and its definately worth doing. It gives a different perspective of the world and increases your instrument appreciation immensely. My favourite part was definately the (simulated) total electrical failure! Landing with partial runway light failure was also fun. Scariest bit was the demonstrated (you won't be asked to do it) EFATO - feels like falling into a black hole...