A thread on reddit reminded me that they included incest as a part of Sarevok's new characterization. Honestly intentional character assassination to prime players to absolutely despise Sarevok and Viconia is really the only way to explain it. If Larian's motivations weren't to elicit such a response from players who encounter them with such portrayals, then their drastic changes to their previously established endings and characterizations really don't make a lick of sense