> I did not find this api to be significantly better for many use cases than writing threads and communicating over a concurrent queue.

The problem with using OS threads, you run into scaling problems due to Little's law. On the JVM we can use virtual threads, which don't run into that limitation, but the JVM can implement user-mode threads more efficiently than low-level languages can for several reasons (the JIT can see through all virtual calls, the JVM has helpful restrictions on pointers into the stack, and good GCs make memory management very cheap in exchange for a higher RAM footprint). So if you want scalability, low-level languages need other solutions.