And if that blog is a newspaper or other aggregator? What makes the RSS feed of the CNN front page fine, but not the RSS feed of the YouTube front page?

There's really no difference. Media companies all aggressively optimize for engagement, often to the point of A/B testing headlines.

There’s a huge difference. Everyone sees the same front page on CNN, or HN for that matter. Nobody sees the same page twice on YouTube or TikTok. That’s a fundamental distinction between human curated media (even with A/B testing), versus machine curated media.