The problem isn't that it hides away the machinery. The problem is that it hides some things, but not everything. Certainly a lot of stuff hides behind await/async. But as a naive developer who is used to real threads and green threads, I expected there would be some wait to await on a real thread and all the async stuff would just happen... but instead, if you await, actually you've got to be async too. If you had to write your async code where you gave an eventloop a FD and a callback to run when it was ready, that would be more explicit, IMHO... but it would be so wordy that it would only get used under extreme duress... I've worked on those code bases and they can do amazing things, but if there's any complexity it quickly becomes not worth it.

Green threads are better (IMHO), because they actually do hide all the machinery. As a developer in a language with mature green threads (Erlang), I don't have to know about the machinery[1], I just write code that blocks from my perspective and BEAM makes magic happen. As I understand it, that's the model for Java's Project Loom aka Java Green Threads 2: 2 Green 2 Threads. The first release had some issues with the machinery, but I think I read the second release was much better, and I haven't seen much since... I'm not a Cafe Babe, so I don't follow Java that closely.

[1] It's always nice to know about the machinery, but I don't have to know about it, and I was able to get started pretty quick and figure out the machinery later.