Why does YouTube recommend some videos and not others?

There is no queue and no leaderboard. When someone opens YouTube, the system assembles a page for that individual by scoring candidate videos against their own history, and your video either wins a slot on that page or it does not. This is why two channels with identical subscriber counts get wildly different reach, and why asking why YouTube is not promoting my video is the wrong shape of question. The right one is: which viewer is this video obviously the next thing for?

Your traffic sources report answers that, and it is the most under-read screen in Studio. A Margalla Trail 5 hiking video that arrives mostly through Suggested is being served beside other Islamabad hiking content, so the system has placed you in a topic it understands and you should make more of the same. Arriving mostly through Search means people are typing a question and finding you, which is slower but far more durable. Arriving mostly through Browse means your own subscribers are carrying you and you have not broken out yet. Each of those calls for a different next video.

Focus is what makes the prediction possible. A channel that alternates between hiking routes, a cousin's wedding and a phone review has given the system nobody to recommend it to, because no viewer history points at all three. This is the single most common problem we find on Pakistani channels that have been running for a year without traction: the uploads are fine individually and describe no audience collectively.

Click behaviour is only half of it. YouTube also weighs whether people stay, whether they come back, and it runs viewer satisfaction surveys asking directly how a video was. That combination is why clickbait stalls: it wins the click, loses the stay, and the system has a second and third opinion to fall back on.