I’ve been curious about it as well. No one seems to know for certain and we may never know.

Some people seem to hypothesize that the owner got in trouble because they had federated with burggit.moe in the past, which is an instance that hosts content that borders on child pornography from my understanding. The sudden disappearance of vlemmy.net seemed to happen just after the admin said they would have to defederate from them because of legal issues…