Why do you believe that "-" didn't appear as a character on typewriter keyboards? On manual typewriter qwerty keyboards it commonly appeared above the number 6. I.e. Shift 6. Do you know of computer keyboards on which it doesn't appear?

The en-dash (set in pica, or the width of an "n") was always on typewriters, and the em-dash (set in elite, or the width of an "m") doubled as the minus sign. It was the hyphen that came later, when computers eliminated the need to restrict ourselves to two type-widths.