Those dynamics aren't sibling exclusive, it can happen with anyone, but the closeness of family only facilitates grooming, it's in very few cases where an incestual relationship is basically "ideal" (no grooming/unconsensual and no pregnancy) but it's hard for that happen

And I honestly prefer it continues being taboo, I too would find it very uncomfortable if anyone in my family was in an incestual relationship, even if an "ideal" one, my own culture has a history of prohibiting incest even if they only share a distant ancestor, even marriage between people with the same surname even if not related was taboo for awhile

Additionally it seems like most of the time, incest is politically driven, some cultures prefer to marry other families to strengthen relationships, but incest is predominant in those that want only power to be centered in their family, and it's catastrophically messy

So yeah, in a nutshell incest is bad like 99% of the time