The topics I’m talking about are like “master” topics. I didn’t go into these details in my initial post, but this community is a language learning community and the book clubs are “beginner book club”, “intermediate book club”, etc. When a new book is selected via poll in the master topic, it does indeed get it’s own topic (often several) dedicated to that book. But the master topic allows users to track/watch all conversation around the language difficulty they are interested in, including nominations, polls, and schedules. If the master topic was abandoned, there’d be nowhere to organize the nominations and polls, and users would potentially miss out if they happened to miss the new topic being created.
All of this is publicly available if you’re curious to see more detail.