The rewrite in C++ movement was lived in Usenet flamewars, and we were in good path with all the userspace C++ frameworks in OS/2, MS-DOS, Windows, Apple and BeOS until the GNU Manifesto came around and urged everyone to write FOSS code in C.
"Using a language other than C is like using a non-standard feature: it will cause trouble for users. Even if GCC supports the other language, users may find it inconvenient to have to install the compiler for that other language in order to build your program. So please write in C."
Yes but back then you could compile C with a C++ compiler and get the same type checking as in actual C++. There were a few pitfalls but a shared "Clean C" coding style was viable and that's what most of the rewriting effort was focused on.
C++ did add stronger modularity with its public and private member specifiers, namespacing etc. but that was mostly useful on larger projects.
Stuff written about C++ before there was an ISO Standard obviously does not apply after. And, we should know by now how much Richard Stallman's prejudices are worth.
By all means, GNU Coding standards from 2006, 8 years after C++98.
"When you want to use a language that gets compiled and runs at high speed, the best language to use is C. Using another language is like using a non-standard feature: it will cause trouble for users. Even if GCC supports the other language, users may find it inconvenient to have to install the compiler for that other language in order to build your program. For example, if you write your program in C++, people will have to install the GNU C++ compiler in order to compile your program.
C has one other advantage over C++ and other compiled languages: more people know C, so more people will find it easy to read and modify the program if it is written in C.
So in general it is much better to use C, rather than the comparable alternatives."
You emphasize my point so clearly, I need add nothing.
But I will note that GNU Gcc and Gdb are both C++ projects now. Gold, the current GNU linker, started out C++. Are there any other still-relevant GNU projects?
That is now, we were talking about when GNU/Linux started to be relevant and what triggered language choice, versus what was happening in the desktop PC world.
The latest version of the GNU coding standard is much more permissive.
"Using a language other than C is like using a non-standard feature: it will cause trouble for users. Even if GCC supports the other language, users may find it inconvenient to have to install the compiler for that other language in order to build your program. So please write in C."
GNU Coding Standard in 1994, http://web.mit.edu/gnu/doc/html/standards_7.html#SEC12