Their usefulness is very restricted.

What we want instead is:

- general concurrency

- access to any (garbage collected) JS variable/object from any thread.

- a garbage collector that works across all threads.

- no global locking of threads by the runtime system

And then you get into the problem that Python has. The reason why Python has the GIL is that all of those things are really hard to do right in a performant way.

I think JS is making the right call here: a small subset just to engage the extra cores.