I think part of it is that most of Rust sets a really high standard for polish and good design; developers new to the language are often quite impressed by its expressiveness and by the breadth of bug classes it protects you from, once you get over the initial learning curve. (Not always—some developers never grow to like it, either because it's a bad fit for their use case or because they happen to find its particular forms of ceremony especially off-putting—but the success cases are striking.)

And then you start using async, which is less polished and has more awkward design compromises and more footguns that you only find out about at runtime, and it's a bit of a disappointment by comparison, even if some of the problems aren't worse than what you find in competing languages. This is the vibe you get in the Oxide RFDs about things like futurelock, for example.