I think it harkens back to coding's origins on punchcards. Many compilers still give errors along the lines of "Line 500, column 16", so it seems natural to use

I think it harkens back to coding's origins on punchcards. Many compilers still give errors along the lines of "Line 500, column 16", so it seems natural to use a font that incorporates those concepts into its design. But yeah, I can think of a few people who AFAIK do mostly use proportional fonts, and they do just fine. I think it's mainly a path-of-least-resistance thing.