Bcs it sells. Paid readership loves it apparently. Incest trope has always been gaining massive audience in fandom & shipping culture, esp amongst east asian, not just korean. Even japanese media has been so long serving incest in many hentai slop, I've found incest in a lot of manga & anime from early 2000s. That's why korean publisher noticed this and take the opportunity in encouraging BL authors making incest manhwa.

why most korean authors lowk obsessed with incest like everywhere in nowadays is always incest that is "incest" this is *incest"