If generators or embedded devices that don't have threads are indeed the reason for picking one design over the other, the question then becomes why did some languages prioritise those domains over more common ones, even for them?
Indeed, to which the answer is: it's a dirty job, but somebody's got to do it. :) As long as C exists, it's worth trying to improve on what C does without giving up on C's use cases. Of course, that doesn't mean that all use cases are equivalently common, nor does it mean that a language like Rust will ever be as widely used as Java, nor does it mean that Java was wrong for integrating virtual threads (I think they're probably the right solution for a language in Java's domain).
A common theme in rust development is the notion that no one could produce more optimal code by hand. This is a great feature, but in the case of async/await we are sacrificing a lot to get it. To the extent that a user trying to make their first http request with reqwest will now get conflicting documentation and guidance on whether they need tokio and other packages to pull in async.
