As someone that was there, a few things helped C++ adoption, and even then it wasn't without the C vs C++ flamewars that endure to these days.
- At the time, with a few minor differences, C++ was Typescript for C, thus very easy to adopt into existing projects
- Being born on the same birthplace as C and UNIX, meant all C compiler vendors saw as added value to have it as part of their offering, and it was natural that every UNIX SDK also had C++ support available alongside C.
- Apple, Metrowerks, IBM, Borland and Microsoft helped to push C++ adoption, by making it the official way to use application frameworks. MacApp (originally in Object Pascal), PowerPlant, CSet++, Turbo Vision/OWL/VCL, and MFC respectively.
This kept C++ as the language to go for performance in enterprise computing, while Delphi and VB got the "easy" development role, until Java and .NET took over all those frameworks.
Rust doesn't have this kind of industry wide push, even in OSes where it is being embraced like Windows and Android, note that it isn't being pushed as yet another way to write userspace applications, rather low level OS services.