Don't generalized the whole asia simply because of the material you read from Korean Manwha & Japanese Mangas. The rest of asian lgbtq love stories don't always have S.A. & Rape. You need to explore other asian LGBTQ content before saying that. Also, fiction ≠ reality but sometimes some fiction may be inspired from a real life event or experience of an author... we may never know. It might be a cultural thing specifically from a country. You have to understand that asia is made up of a lot of countries and not just East Asia.
P.s. for roles, example, the Philippines has most tops/mostly tops from a survey i think it was from bumble(???) so that might affect why not a lot has verse in korean manwha. In Japanese Mangas however I have seen a lot of verse couples.
I also noticed in manga/manhwa "Boys Love" that there is a huge amount of SA & Rape being used as a plot point in stories. Also, why are most the uke feminine and why don't the couples ever swap sexual positions? You tell me the uke never wants to top? BL is the worst representation of Gay male relationships I've seen in the form of comics and it makes me sad that this might be someone's first taste of Queer romance.