Algorithm, Search & Distribution
Personalisation
Also called: personalization, personalised recommendations
Two people opening YouTube at the same moment get different home pages. Personalisation is the reason: the system builds each feed out of what that person has watched, searched for, subscribed to and skipped, so there is no single ranked chart to climb.
Your video is never competing for one slot. It gets matched to individuals, and the ones it reaches first have a history that looks like your audience. That is why a video can look dead in one account and be everywhere in another.