I know. I was speculating why some website creators prefer dark grey on bright white, as opposed to pitch black on slightly off-white (which I think is easier on the eyes).
Line ghosting [0]. Which can be alleviated with more spacing between lines and a larger font size, but even then I still find it problematic personally. "Ghosting" is a lot less noticeable on light backgrounds, which I think is just how the eyes "work".