A now inactive account likely made them, but that person no longer uses Lemmy. If it wasn't "taken over" it would be unmoderated. Consolidating those under one account is easier on the admin and let's people willing to mod know they can request the community
Trending communities is scuffed and doesnt actually show trending communities. Usually if theres a new community made within the last 2 days it shows there otherwise it shows the most dead communities as they are getting large subscriber activity relative to their MAU
Vacant collects a lot of different kinds of communities ranging from unmoderated ones that havent been taken over yet by a new mod team to ones that are admin started to start getting some content on that subject (usually if thats the case ill be posting in it on my other account)