Rust didn't implement async/await for fun. The team implemented it because it was perhaps the #1 requested feature from users, including me.
You can see it here on HN. What's the #1 comment that always appears on Rust async threads? Invariably it's "why not just use goroutines? That kind of code is so much easier to write!" Now for various reasons M:N threading like in Go doesn't work in Rust. What does work, and offers most of the ergonomics of threads/goroutines, is async/await. That's why the team has prioritized it.
There are people who care less about ergonomics than optimizing every CPU cycle for socket servers. For those people, the focus on getting the ergonomics right before microoptimization of mio and tokio might be frustrating to see. But the overwhelming majority of users just want easy-to-use async I/O. Async/await is an enormous improvement in readability and maintainability over hand-written state machines. Rust would be doing a disservice to its users if it focused on microoptimization of tokio instead.
