Marriage in the world of cultivation is mostly done for the sake of their Family. Forsaking the emotion which they held within their hearts and reaching the top by sacrificing a member of their own Clan.
The World of Cultivation is nothing short of a political power struggle, despite how straightforward it looks the balance it has is nothing but a flimsy line. The Xie Clan, Desolate Clan, Feng (Wind) Clan, and the Mu Clan are just a few examples of such a thing.
There are countless more Clans out there that practices such things, and the ones who does such acts are the startups who send their daughters to the well-establish powers of the world.
They seek protection from stronger families and seek to find a connection that may lead them to a greater future. Such an act is not even vile as it was common practice, it is only vile to those who see it as so.