Remember that writing programs on terminals was a
relative latecomer --
FORTRAN was designed for punched cards.
Remember that FORTRAN also was a latecomer. It was a shock
to convert from the full character set of the Flexowriters at
Whirlwind to the rebarbative upper-case-only of the 704.
In that vein, there was a period when the Chicago Manual Style
disparaged uppercase text, with an exception being made for
computer programs, which of course should be presented in
upper case.
Doug