IIRC, they went with async/await because it could be implemented through desugaring in the compiler using a technique similar to what they had implemented a few

IIRC, they went with async/await because it could be implemented through desugaring in the compiler using a technique similar to what they had implemented a few months earlier with IEnumerable. That is to say, the team was thinking about desugaring at the time the need for asynchronous functions arose and they were not thinking about CSP. Remember that C# was in production at the time and they needed something that would not potentially upset the world.