Well for one thing, “accounts” is nearly a meaningless number. Even Reddit finally acknowledged that and is starting to abolish them. I personally have had several accounts (kbin.earth, startrek.website, discuss.online), and some people here have roughly one account per instances - which since Lemmy has not federated moderation reports was basically essential (see e.g. this post).

This btw messes with the stats even for “active” accounts, by inflating them so that multiple accounts get counted even though representing fewer people.

Though in contrast, someone who made an account once 3 years ago, then left and never returned… this means next to nothing, making the https://fedidb.com website not nearly as useful for that purpose (instead it would track mainly “older” instances, except even there it does not work for that purpose, since e.g. lemm.ee is of course missing).

Also, I notice that hexbear.net is missing too, and I recall that at least one point it was one of the largest instances. Note that it is missing from both websites though, leaving both of them imprecise, yet it would seem not equally so.