Because as much as I like Rust, it doesn't provide the IDE tooling for mixing language development with Java and .NET stacks, the seamless tooling that for creating COM/UWP components, something like Unreal or Unity for weekend coding hobbies, still builds slower than C++ because cargo doesn't support yet binary dependencies.

For writing memory safe code I already have .NET and JVM set of programming languages, so when I need to go outside of these platforms, I rather pick the tool that provides zero attrition with the existing tooling.

These are all issues that will be fixed, but they aren't yet there.