I am not an expert in python but I feel that the JS model where everything is on the event loop and there is no actual threads seem better for a dynamic language. A lot of parallelization can be achieved with web-workers, but of course at the cost of relying on copying memory between workers (ie no shared memory).

There have been some proposals to add full shared memory constructs (SharedArrayBuffer) and synchronization (Atomics) mechanisms, but they are special constructs and don't work with normal javascript objects. Quite limited but provide full parallelism for things that usually need it (buffers).

One thing people often forget is that thread-safe data structures are usually a lot slower than single-threaded one, everything in JS is single threaded and in the event loop, but if you really need it there are some scape hatches.

I don't know, this just feels better and simpler? If you really need to you can go down to a lower level language for full memory sharing data structures.