I don't think a sleeper service is a requirement for EK. Most pax will be on different time zones based on their origin or destination so it won't be their night time even if the clock says so at that point.

Putting lights off etc may discourage those who want to stay awake from getting up and walking around, or having a chat with their companion.

On the other side, eyemasks and earplugs are available for those that can't sleep with the light on or a bit back ground noise.