As I mentioned on the Reddit thread,

This is quite understandable when you know the history behind how C++ coroutines came to be.

They were initially proposed by Microsoft, based on a C++/CX extension, that was inspired by .NET async/await implementation, as the WinRT runtime was designed to only support asynchronous code.

Thus if one knows how the .NET compiler and runtime magic works, including custom awaitable types, there will be some common bridges to how C++ co-routines ended up looking like.