The black background with light grey and green text, and the use of a fixed width font are intended as an homage to old monochrome computer screens, and to text-based computing (admittedly, my own life was filled more with amber monochrome screens than with green ones, but the green ones were still there, and green is far more readily available than amber as a terminal colour these days). My computing is still heavily text-based, and uses a similar colour scheme (perhaps because I'm a little nostalgic).

Also, I find it rather visually jarring to jump between the appearance of an old console and that of a glowing piece of paper, and this style helps me avoid that.