I think it’s because C++ programmers tend to define themselves by the domain they work in. Game developer, embedded systems engineer, firmware developer, etc.
I feel like it implies "it's harder to make a word out of 'C++' than it is for things that already naturally evolved as words people say like 'Ruby', 'Python', or 'Rust'".
it suddenly struck me that there has never, AFAIK, a single-word noun for a C++ programmer. not sure what, if anything, this implies.