3 years aligns with the Great API Debacle and protests on Reddit. It's when the Fediverse first started being discussed on many other sites and people were urged to shift over; certainly that's when I came over.

For any number of reasons, however, not everyone stuck around. Some were hoping for a larger shift-over that never materialized. Some found the smaller population and lack of niche communities they had enjoyed. Some were turned off by the political extremism and hate speech coming from some communities.

I don't have any issue with the accounts being left up, but I do think there ought to be a formal ruleset for opening up a community to new mods if the moderators go MIA.

Mod users? They’re probably just used for moderation and not posting. Lots of mods use alt accounts to moderate to avoid having their identities found out so they can continue to abuse users and censor content with no consequences to their regular account.