So if you believe Facebook sells your information, then you also believe that Facebook is directly lying about it on a help page about that specific topic. Sometimes conspiracy theories are true, so it's not impossible that that's what happening, but it's not like Facebook is openly selling your information.
Until 2014 or so an app could request permission to view almost any data a user stores on Facebook. That's not great, but hey, you could argue it's not Facebook's fault that people don't understand permission prompts (I'd disagree with you, but...). But those same prompts allowed users to give away their friend's data, so absolutely anyone you're friends with could take some stupid personality test and give away your information in the process, and there was no way you'd even know.
Facebook said that they don't sell your information. Which is true -- they aren't a data broker. But they implicitly state that your data is shared, subject to the limited controls available. You cannot stop Amazon and Facebook from sharing, for example.
But what if you do?
That's not true.
I have never seen Facebook allowing large scale harvesting of their data.
And it would qualify as data breaches in places like EU which do not tolerate this sort of thing.
I'm no facebook fan by the way, but there's no reason for facebook to sell their most important asset when they can allow you to pay to use it, without ever seeing it
Facebook lets companies bid for ads to show you, based on Facebook’s data about your interests and demographics. If you never engage with the ads there is no information leakage.
It’s the difference between telling a random person “I’ll tell my gay friends about your party” and “Did you know that Bob is dating Steve?”.