The Qunari are dragon descendants. Incredibly far, but dragon blood is powerful. Dragons are, after all, alpha predators and survivors.
Sometimes that survival comes in secreting away a people born from dragons so that they live on not as giant, scaled beasts but humanoid, dark-hued people.
It's the horns that give them away.
But it's time that erodes that truth to a legend, a far-fetched theory among the Ben-Hassrath. It wouldn't do for people to be aware of this, of the secret of their people, and so it is locked away in their secrets, their intrigue.
But it's always the Ben-Hassrath that instruct the Tammassrans on who will mate with who.
It won't do for the blood to breed too thickly.
That means a chaotic force that destabilizes everything they've protected all these years, a complete waste of resources.
Unless they reshape that force into their own image.
Cue Iron Bull.