You’re thinking of software that is being written today. GP is talking about software we use every day in every device on the planet that hasn’t changed since it was written 30+ years ago.

What is this software? E.g. Linux is 33 years old; barely a few percent of Linux 1.0 remains in a modern kernel, if we count lines of code.

Maybe GNU Emacs has a larger percentage remaining intact; at least it retains some architectural idiosyncrasies from 1980s.

As of Fortran, modern Fortran is a pretty nice and rich language, very unlike the Fortran-77 I wrote at high school.