I wish they would at least include the japanese cc subtitles. They must already exist so I don't understand why they can't just be packaged along with the other subs.
From what I understand, the written translation, in the form of subtitles, that accompanies the original language audio are have their own copyright and are licensed separately to the translated audio version and its closed captions. If they were to include the dubbed audio alongside the translated subtitles, to be compliant with all applicable copyrights, they would be on the hook for licensing costs twice over, which is why the legitimate streaming sites rarely do that, nor do they even expose such a dual-mode capability via the user interface.