There are ads on HN (the "xyz is hiring", and I suspect a non-zero number of articles posted/promoted to the front page are paid ads made to look like content.
You can gauge user interest by, for example, counting page views. You don't need to fingerprint users, create a catalog of all articles they view, try to guess their interest in certain topics using "AI", and do all the other absurdity that they think they "need" to do now.
If it ever starts to not benefit ycombinator, then the aite goes away.