LGBTQ and BL, in literature, movies and series is by definition a distinct "genre" - and has been recognized as such for decades.
GENRE: a category of artistic, musical, or literary composition characterized by a particular style, form, or content.
Further, it is used by all streaming services (Viki, iQiyi, etc,) as a genre to improve search.
Again, one must wonder if the exclusion of GagaOOlala is because it is a provider of LGBTQ/BL/GL content. Frankly, I just wish MDL would say why it hasn't been added - perhaps they have a very logical or contractual reason?