Question: Why do most programmers/developers use a dark theme while writing software/code?

Answer: Because light attracts bugs.

@nixCraft It's 'cos CRTs used to be not-very-good at showing that much non-black on the screen - the picture changed size as you put up more non-black and it flickered.

Black on white, is, of course, easier to read. There's a reason why black ink on white paper is more common than white ink on black paper.

@nixCraft @TimWardCam I feel like paper might be a bad example? I mean in that case itโ€™s because of how pigments work.