This only happened because a team of professional journalists worked on the story for months, despite Facebook denials and stonewalling:

https://www.snopes.com/news/2019/10/11/pro-trump-outlet-link...

https://www.snopes.com/news/2019/11/12/bl-fake-profiles/

https://www.snopes.com/news/2019/12/13/facebook-bl-cib/

https://www.snopes.com/news/2019/12/20/facebook-removes-the-...