YSK: Subscriber count on communities only show the numbers of users subscribed from your specific instance. The real number might be much larger than you think.
Edit: Why YSK: New users of Lemmy can find the number low and think that a community is dead or inactive, when infact it might be a thriving place with a lot of activity.
Are you sure? I don't think so. It shows users with data on the instance. A one subscriber instance will still show hundreds or thousands depending on how much federated content there is.