Blame Knuth. Afaik the font used simulates closely the typesetting of the original art of programming edition that was printed using hot metal typesetting on an

Blame Knuth. Afaik the font used simulates closely the typesetting of the original art of programming edition that was printed using hot metal typesetting on an old monotype machine. Later these machines were eliminated for more modern techniques but he didn’t like the look so developed TeX to achieve a fidelity with those machines for art of computer programming later editions and new volumes. It has been almost universally adopted in academia since.