A topic page like #reels matters here when it has a real visual scene behind it: recognizable card styles, recurring creators, and more than one post worth opening.
A strong topic page shows more than popularity. It shows a visual cluster: the kind of frames, creators, and post patterns that make the topic readable as a scene.
A weak topic page is just a loose pile of posts with no coherent surface. Those pages make poor feed exits, so the build tries not to keep them.