A lot of these reasons. I'm naturally nocturnal, I've been trying to transition back to being a day person for years but can't seem to make it work-- I've always been exhausted during the day when working a day job and I'd stay up late on the weekends. Now that I work at home and can set my own hours, I work all night and sleep during the day. I love the silence especially, the lack of traffic if I have to run to the grocery or drug store, and how amazingly beautiful it is to go walking right as dawn is breaking and everything is covered in dew. I'd miss those things immensely if I could manage to keep a normal person's schedule.
I'd have a lot more active social life, though, if I did that. Not a lot of people can keep pace with you when you're most wide awake at 2am.