Implementing coroutine requires to change to the code generator, the runtime and the garbage collectors and there is no general consensus on the way to implemen

Implementing coroutine requires to change to the code generator, the runtime and the garbage collectors and there is no general consensus on the way to implement them efficiently => this requires a huge investment in engineering. For Rust, one of the feature of Rust is to have a minimal runtime, so using a compiler transformation seems a good fit. For C#, Microsoft has a limited number of people working on the runtime of DotNet. Async/await was developed at the same time DotNet was transitioning to DotNet Core which also requires massive engineering, so it was about priority. The future will tell if at some point coroutine will be added to DotNet.