Recent example, while Android has adopted Rust for replacing their bluetooth stack, the newly introduced Android Games Development SDK focus on C and C++.

Or Microsoft, despite all their security speech, Azure Sphere OS and RTOS only support C on the official SDK, and the new WinUI components are all based on C++.

And naturally anyone wanting to contribute to the Rust compilers, most likely will need to brush up their C++ skills if they intend to mess with GCC or LLVM internals.