> It gets multiple book level treatment in Japanese (if you’re in Japan, please ask about the keigo section at a decent bookstore), and I am familiar with at least a few post-graduate papers on the topic.

There are entire PhD theses on aspects of English (or Spanish, German, Italian, French, Russian, ...) grammar too. That doesn't mean that people can not learn to use the aspect in question intuitively. It just means that it's difficult to provide an explanation for this behaviour.