An open network for secure, decentralized communication
Have you checked on Element to see if the rooms appear there? Generally, when you leave a room on Matrix the homeserver you're on still holds a copy of that room that is cached until you "Forget" the room (and on the backend, its completely removed when all users on the homeserver have left the room AFAIK).
Matrix does not delete your messages from the room whenever you leave a room though. What I don't know is what happens when your account is deleted, however.
They do not appear in Element. I've never seen "historical" rooms there.
Sounds like there's a reason why it's nowhere called "delete room"
What you see is the historic version, you should not see any messages after you leave.
This can be shown because the room is not immediatly deleted, it just has 0 members and should be purged later when there are free resources on the server, as deletion and clearing up the database takes some work. Actually most used Matrix server, Synapse, is also very bad at clearing after itself so most admins currently need to write scripts to clear those rooms.
Empty rooms makes sense from the protocol perspective, as they can be used to store data for something other than chat. Still we should have more ways to tweak the behavior.
Last event I saw in those rooms was that I left.
There were rooms older than a year :/