While it would be nice to have the language be able to do it, the fact that you can't today leads to some tidy separation of concerns for parallelization. For instance, many people I've talked to use things like Spark or dask to get high scale on data processing tasks. That means that all of the management of distributed jobs is handled through an easily googleable framework that your ops team can manage, as opposed to needing to build all of that yourself.

I see this as being a nice stopgap solution for those who are too big for single-threaded but not big enough to need Spark.