It’s entirely possible that my timing was just bad for Mastodon and good for Lemmy. The fact that I could jump on Boost and have an extremely familiar experience was a big plus. Bluesky was more similar in terms of migration experience to Lemmy than Mastodon was.
The other issue is that in a forum site you follow topics, where on a microblog site you follow people. The topics are here on Lemmy (to some extent), even if the people aren’t, but I don’t really care about the individual contributors as much. The people I wanted to follow for microblogging went to Bluesky, and that matters a lot more there.
Yeah, on reflection, I think that’s the crux of it. There were some users from a more tight knit subreddit that I got to know well, but we all moved to discord a few years back. I miss some of the more active niche subreddits, but otherwise Lemmy replaced it very easily.