Because not everyone wants or can write any of them? If people like Rust and want to write and read Rust, then it makes sense to write it in Rust. Not in “any of them”. And when they see other projects written in Rust, it makes sense to review it, look into, adapt the code written in Rust. Not in any of the other languages, because the project is in Rust. Let’s go back again to understand what my point was. I try to be clear as possible. The GNU tools are written in C. Only programmers who understand and can write in C can understand and write in C. But look… someone rewrote the GNU tools in Rust. Not in another language. In must be my lucky day, because Rust is my favorite and only language I write (that’s not true BTW, but that’s is besides). I loooove writing in Rust and immadiately open it up, look into, I can read and write in Rust. Not in another language.