Did you join the forums just to ask this question specifically?
Also you writing is very disjointed. Are you asking why there's a category for 'boy love' and none for 'girl love'? If so, I agree there should be a category for the two genres.
However, I hold some opinions and concerns on the subject.
If Tapas does decide to add the additional category I would also hope they would choose to use more appropriate western terms for both categories for at least their English side of the site. Terms that would not be misinterpreted as pedophile catering by those unfamiliar with the genres. Lolita fashion also suffers this issue so it's not just limited to Asian terms for comics and writing.
Instead of BL/GL or Yaoi/Yuri, perhaps Gay Romance, Lesbian Romance, YA Gay, YA Lesbian, or some other western literary accepted form of title for the genres.
This will likely always be a long standing problem when it comes to the two genres until there is a term that requires no explanation beyond the words used to describe it and a clear divide between YA versus Adult materials of these reading preferences. I feel it would be a step in the right direction though when it comes to making the genres more widely acceptable and less likely to end up creating conflict or debates with misunderstandings.
As for mentions of a third category for Bi or Trans, I do think just the three categories of Romance, Gay Romance, and Lesbian Romance should cover those two spectrum as Bi would read all three, and Trans would be able to relate to at least to one of those three.
