Game engines (the thing that C# runs on top of) are written in C++. As is the C#/.NET runtime. As is anything that requires careful management of memory for performance. Application code is perfectly reasonably written in managed languages, but not so for the things that run underneath.
There's nothing inherent about C++ that makes it more suited than Rust for game engines though, Rust supports careful management of memory too. Of course, nothing besides inertia (i.e. Libs, existing code, etc.). And that of course is more than big enough of a reason to stick with it.
Rust supports careful management of memory at the expense of unsafety, at which point that particular area of the code offers no benefit over C/C++, let alone value in a rewrite. There is no type system for reinterpreting bits of memory.
And for the safe parts, the posts that I've read from people who have spent a non-trivial amount of effort with the language do not paint a clear picture either on whether there was really a benefit to the language overall.
So to say that "the world has moved on" in light of all of this is pure hubris.
