So there’s really three forces at play in making C++ the standard:
1) The Microsoft ecosystem. They literally stopped supporting C by not adopting the C99 standard in their compiler. If you wanted any modern convenience, you had to compile in C++ mode. New APIs like Direct3D were theoretically accessible from C (via COM) but in practice designed for C++.
2) Better compilers and more CPU cycles to spare. You could actually count on the compiler to do the right thing often enough.
3) Seamless gradual adoption for C developers.
Rust has a good compiler, but it lacks that big ticket ecosystem push and is not entirely trivial for C++ developers to adopt.