Have you ever thought it odd that when night falls in Azeroth, the stars appear, the sky darkens, but the landscape itself remains as bright as it was in broad daylight? Once upon a time, the nights in WoW
looked something like the above screenshot. I can't pinpoint the source since it was so many years ago, but the original reasoning was it changed so people who could only play during the night wouldn't have to always play in the dark. The current official line
is that it was purely an art decision.
There have been innumerable threads
on the official forums pleading for the return of dark nights. Blizzard has been listening and in patch 5.4 they added a "test case" for darker nights, but only in Stormwind, Orgrimmar, and Vale of Eternal Blossoms. The difference is there, but you need to compare before and after screenshots to really notice it. It still doesn't scream "night has fallen."
Despite the fact that I'm a very "technical" player and I spend a lot of my time concerned with numbers and what trinkets to use, I am a total atmosphere junkie when it comes to video games. I scoff whenever I hear another person say they play with their sound turned off, such a thing would be sacrilege for me, as the music
and sound add so much to the atmosphere. I feel the same way about the graphics.
I can definitely see the downsides to having darker nights for people who can only play the game at those hours, and I'm betting Blizzard is worried about players being able to see monsters and quest objects easily at all times of the day. If you ask me, the best compromise is to make dark nights a graphics setting and leave it turned off by default. I don't think we will ever see nights as dark as they used to be without such an option.