The dirty secret of the Internet - going back decades - is that it's concept of moderation mostly relies upon unstated or understated rules half-enforced and adjudicated by volunteers or underpaid contractors with the power of judge, jury, and executioner. This is arguably by design: the vast majority of what moderators are dealing with is spam, which has the properties of being cheap to execute and difficult to filter for. Hence, anti-spam efforts are swift and merciless. More modern efforts to deal with things like foreign election interference and fake news are arguably extensions of this same ongoing effort to summarily hang and execute spammers.
Facebook is not alone in this either: Google's done it from the very beginning and their death penalty stings far harder. There's a few exceptions to this, such as Wikipedia's ArbCom or other collaborative Free Software projects with code-of-conduct rules and moderator transparency. However, even those platforms will summarily execute spammers.