To get philosophical I won’t say that I “know” it’s happening. Most of the world consists of things I don’t know about. The best I can do is build a mental model based on what I do know.
Why aren't bad actors using it in the wild? I think it's a combination of them being technically unsophisticated and conservative, propaganda not actually working nearly as well as people like to think it does, and lack of detection of competent actors (things like StyleGAN being used for fake FB profiles are detected through carelessness like leaving the faces exactly aligned).