When I look at historical cases, it seems different from a case today. If I’m a programmer in the 60s wanting async in my “low level language,” what I actually want is to make some of the highest level languages available at the time even more high level in their IO abstractions. As I understand it, C was a high-level language when it was invented, as opposed to assembly with macros. People wanting to add async were extending the state of the art for high level abstraction.
A language doing it today is doing it in the context of an ecosystem where even higher level languages exist and they have made the choice to target a lower level of abstraction.
People are putting C++20 co-routines to good use in embedded systems, in scenarios where the language runtime with some additional glue layers, is the OS for all practical purposes.
And GPGPUs as well, like senders/receivers whose main sponsor is NVidia.
A language doing it today is doing it in the context of an ecosystem where even higher level languages exist and they have made the choice to target a lower level of abstraction.