The solution is to build up more attractive alternatives of those communities elsewhere, not endlessly campaign the existing users to just drop them.
Agreed. Maybe I should try creating and managing a community some day. (hopefully this didn't come off as sarcastic)
The current fedidb stats, to me, state that 488 people is, colloquially speaking, nobody.
This is a wildly misleading and unfair comparison. Let's take the Trump verdict as an example. The most upvoted post about this had ~2700 upvotes. But that's only 6% of the MAU! Is that "nobody"? Obviously not. 2k upvotes is a huge deal on a rather small community like Lemmy. How often do you see posts with more than 3k upvotes?
~500 upvotes is already a moderately large number of upvotes. You need to compare this number with how many upvotes a post typically gets.