Its a good goto trope of having an attractive villain both for
1. Just wanting to draw some exploitive traits because who cares if you take it to an extreme they're typically characters of an extreme personality
2. Its always an easy setup for a character who is vainly nice/attractive at first but the more you see of them the more obvious that their positive feature are just a thin veil and their true ugliness/villainous ways
An absolute trope in both cases but hey if it ain't broke don't fix a good system of visual storytelling.