[IshKebab]

I haven't read the article but in my experience FORTRAN is used because a lot of really complex numerical routines were written years ago by really smart people in FORTRAN and nobody really wants to rewrite them. There are exceptions - the basic LAPACK stuff has modern alternatives (e.g. Eigen for C++, nalgebra for Rust).

But there are a ton of more specialist libraries, e.g. ARPACK that people probably aren't going to rewrite.

That said, there's a FORTRAN to C transpiler that works pretty well. I used it when I needed ARPACK and didn't want to deal with FORTRAN.