Well, see, Mastodon has had a functional monopoly on ActivityPub usage, and also Mastodon users are able to and do engage with Lemmy communities. Mastodon’s share of AP usage going down is of interest because the fediverse has a monoculture issue, and that’s a thing people on a forum like this one should keep in mind.
For the confused: https://www.youtube.com/watch?v=C0hETFY67F0