What this shows us is that more people are joining lemmy, but even more people are either leaving or going into lurker mode, as Lemmy only counts people who have commented or posted in that time period as active users, whereas most social media counts any activity while logged in as active. You have to realize that people who use reddit as Google search results don't usually interact with the content there and most won't even make an account.

On the upside, with fewer people, it's easy to get noticed here just by contributing good content since you don't really get drowned out here because of the democratic upvote based sorting instead of black box personalized recommendation algorithms. So with relatively low amount of effort, you can make sure your content is being seen instead of relying on analytics and metrics.

The last thing to in mind that Lemmy is only one aspect of ActivityPub, and Mastodon's growth is currently the highest right now because of the ecosystem created by the whale fall of Twitter, which indirectly grows Lemmy as Mastodon users can post directly to federated Lemmy communities.