I think there could be a pretty simple reason to keep people in the dark about how the AI works. If the rules are public you will end up with people trying to optimize their stuff to make the most money, so likely pretty much uniform content and that gets boring quickly..
If you keep people in the dark, everybody tries different things and that allows to meet different advertisers needs and keeps the platform more interesting….
Same with HR, when you know the rules everybody presents the same optimized cv, better to keep the rules secret and get “possibly” better results…
You can go to YouTube and watch videos all day for “free”. However, nothing in life is free. The AI is not advertiser friendly, so what is YouTube developing? With how much the AI has changed they are progressing towards something, but what? It would almost be worth to write an AI that could learn the YouTube AI, and see what it’s patterns are.