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It's different audiences, BL is its own thing and for straight women that want to see guy on guy action. I remember reading some female mangaka from the 70s/80s writing about why she wrote that kind of stuff and she said simply a good looking guy is hot, two good looking guys with each other is more hot.
There is some crossover though, I have a pixiv account and one day I noticed some BL coming into my feed on the site. It confused the hell out of me and I checked and the artist did some ane-shouta stuff that I liked and that's why I subscribed to her.
This is mostly a problem in the west though, as I noticed that in Japan people usually don't dunk on each others fetishes and interests as much as the west. I went to comiket when I went to japan a few years ago and saw a bara(homosexual male) doujin manga section on the floor on the same floor as straight erodoujin; it would be hard to imagine that happen in an american context as anything aimed to straight men is demonized by so many "rights" groups and said activists would show up and start a scene.