Again- it is because she is one of the primary antagonist. If she were a side character I would agree, but since she is a major villian I'd posit there should be significant variation in her pathings.
She isn't some side character with a fetish attached to her like Grey-hide (big dick + swinging), Liurial (maledom), Draith (male x male bottom), Cla-min (shortstack, romance, harem, breeding), or X'zaratl (futa + poly), Skodred (dwarf???), Shaya (prostitution), Cilonia (a duality of domination), Helenya (Rape....I guess).
Rowans relationship to the twins in terms of power dynamic practically defines the entire experience of the game- and a large part of that is the sexual dynamic. She isn't just some kink path- she is one of the primary antagonists.
Some players want to beat her down, dominate her, and have fun with her before the game is over. Just like some players want to be submissive to her, let her control their lives, and ruin their relationship with their wife.