Pre-Rust "serious C++ folks" used it because it was the best option if you wanted essentially zero performance overhead no heavy runtime and GC spikes. They didn't like the lack of memory safety but it was seen as an unfortunate but necessary trade-off.

These days most of the sensible people have moved from C++ to Rust and so the "serious C++ folks" are an entirely different distribution of people who are much more inclined to think memory safety isn't a big deal and you just have to not make mistakes.