Some spots just have nothing during the day but light up at night. If you want to fish them, then you do it. I enjoy the sunset run as much as anyone else, but night is when you can focus and, as others have said, much less people around, which makes it easier to focus for me.

it's quiet, no people, cool temps, peaceful...and I like it...something about creeping around in the dark and sticking bass does it for me.
I'm ready for a break now though....work and family are suffering.
June and fall are bigtime for the nights for me....I lay off a bit in July and Aug. to focus on the things neglected above.

I fish at night out of convenience, and now that I found a couple of suckers to go with me, I go more often. I have a one and three year old, it's difficult to justify time away from them and the wife when they are awake and I'm not working is near impossible. The fact that the fishing turns on after dark.......just a BONUS!
Other obvious reasons have been posted over and over, I think the most appealing is elbow room.