Facebook posts their content, and in return the agencies can run ads and beg for subscriptions from the traffic that Facebook drives to them. They both benefit.
People post links to their content. Not the content itself - this is a very strong misconception that has been at the heart of all of these bills and laws (Australia, this one, etc.) - from the start, there seems to be a determination to treat posting a link with maybe a headline and one sentence of preview as being the exact same thing as posting the entire article, which is incorrect and ludicrous!
Facebook doesn't post anything. These websites post things to their own pages and individuals post links to news articles.