Hm, I think I have seen photos of books that included the genre/subgenre/"tags" on the backcover, though not in the blurb (if that had a blurb, rather than testimonials), but near the bottom.

So why does traditional publishing decline to spell out the subgenre, then? It seems like a good idea to me. (As opposed to putting testimonials on the back of a book instead of a blurb, which they do...)