One of the co-authors has over 300,000 subscribers on YouTube where she has been posting content about sci-fi and YA books for years. So she already had a fanbase of sci-fi book readers who were excited to read whatever she wrote.

For some reason, the article didn’t mention that one of the coauthors has over 300,000 subscribers on YouTube. Her videos are mainly about YA scifi books, so her fans would naturally be interested in buying a scifi book that she cowrote.