Incest brother x sister is written almost exclusively by single children or children with no other-sex siblings. They think it's herotic because they never experienced the biological block that people grown in mixed environments had.
People that had other-sex siblings know it's disgusting, repulsive, because you are biologically wired to not find sibling or other family member sensual.
Extreme rare exception are for perverts like Freud that wanted to fuck his mother and so he projected his perversion on everyone else to dim his own guilt.
Normal people think that is disgusting, that's why you never see it, and thank god keep it that fucking way.
Incest should be only with "step" relatives, which means it is an artificial and not biological relationship that won't potentially create children with genetical defects.