So a certain portion of humanity are programers. So what, right? Not a great number anyhow. Ultimately, who cares? Here's the catch. When the day to day routine pushes you somewhere, you accomodate. People working countless hours on computers know that the light coming from the screen is mostly too much in the average case.
In the old days libraries showed you old newspapers in dark screens with the printed letters in white. That was only convenient. Why would anyone want the opposite? Using a white background and black letters in a pc has just few reasons. Two. 1. Looks like ink on paper. 2. Contrast is good. But, what if ...
Some would advocate that a terminal, a text editor, a browser or any artifact that proritizes a dark background could be easier on our eyes.
That is why one could not quite wrap the idea that a vim tutorial is made in the same old contrast color of black over white. Well never mind. Maybe the author uses a text browser such as w3m. And I can too.