Comment by pjmlp

You missed the part that GNOME was started due to differences with KDE licensing, and original FSF was against C++ due to religious reasons, and even if KDE/QT license had been GPL compatible, they would not adopted it.

If you look around outside Linux world, everyone was going into C++, PC world with OS/2, MS-DOS and Windows, Apple, Epoch (later Symbian), BeOS,.... UNIX was playing with CORBA, OpenInventor,....

Here the original version of the GNU Manifesto,

"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."

The GNU Coding Standard in 1994, http://web.mit.edu/gnu/doc/html/standards_7.html#SEC12

Moving a bit forward to 1998, when GNOME 1.0 was still being made ready,

"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. For example, if you write your program in C++, people will have to install the C++ compiler in order to compile your program. Thus, it is better if you write in C. "

https://www.ime.usp.br/~jose/standards.html#SEC9

Yes, the actual version is a bit more welcoming to programming language variety,

https://www.gnu.org/prep/standards/html_node/Source-Language...