To be honest, 99% of those have no activity.
People created communities so they would exist in case there was a need.
It's better to look at how many posts and comments Lemmy has to understand "activity" . I wish the "active user" counts included people who lurk and just upvote / downvote, because most users are lurkers and they don't show up in the stats.
We are probably at least double the amount of users that show as active right now.