Organic reach is granted, not purchased. A platform decides to show a piece of content to people because signals suggest they will want to watch it — watch-through, replays, shares, comments.
Its defining property is that it compounds and persists. A clip that performs can keep accumulating views long after it was posted, and it costs nothing further to keep it alive.
Its defining weakness is unpredictability. Organic reach cannot be reliably scheduled or guaranteed for a given date, which is precisely what paid distribution is good at.