Wouldn’t Facebook have to register as a PAC to do this?
You seem to be forgetting that the satanic elite don't have to do anything they don't want to do. Laws are only for the "little people" in Shrillery's terms.
Facebook has an API (google it) that allows customers (and no, that is not you, Facebook user - it is advertisers, political campaigns, etc.) that allows programmers to write code against all Facebook profile data (that’s you, Facebook user, your profile - all the info you gave them including your Likes and Dislikes, ad infinitum).
This API is open to anyone who is buying Facebook product - that is, user profile data.
Some programmers write better code than others to hitch up to the API.
Cambridge Analytics just did it better.