Reddit grew alot when it got known that they did AMAs with celebrities and world leaders. All the tabloids would report on it. It’s difficult for Lemmy or even Reddit to repeat that without having someone in a paid full-time position to arrange and facilitate the interview.
Another thing is the size of the userbase. It got to the point that the sources for specific news were on Reddit, making it the first to have details on the stories, so it was often referenced in actual news outlets.