Rust is doing well because it fills a usecase that has been crying out for a new solution for decades. Low level systems programming - kernels, microcontrollers, high performance applications - have basically had to be written in C or C++. Sure, under some circumstances people can get away with writing performance critical apps in other things, but you can't really write a real world OS kernel in anything else.

Rust brings a new set of tools and tricks and safety to an important use case that has had no movement for such a long time. The only real advancement has been smart pointers and "modern" C++, but while they are an improvement they also contribute to C++ being a bag of all the features.