Ok, I'll bite. What's that reason? Because as long as the contrast is there, there is no obvious reason why using that color scheme would lead to less importance or popularity.
Because objective studies have repeatedly shown it's harder to read white text on a black screen, compared to the dark-on-light text that 99.9% of everything else on the planet uses.
It's a way of sending the message, "It's my site, not yours. I don't care if you don't find it legible. Everybody else is wrong, and I'm right."
