Going from single node to multi core doesn't introduce nearly the amount of complexity that making a distributed system does. Recommending that for someone who

Going from single node to multi core doesn't introduce nearly the amount of complexity that making a distributed system does. Recommending that for someone who wants to use more than 1 core on their machine is not a reasonable recommendation. You're not wrong that you might wind up there, at the end, but doing that for the first step is too heavy unless you have a runtime to support those complexities more easily, as in e.g. BEAM.