The new AskLibO system is configured to automatically close solved questions 30 days after the last post. Shout out if you object to that behavior!
We’ll see in a month whether that works or not. Judging by a quick search imported questions from AskBot are not covered yet. Probably the migration bumped the internal acceptance date.
Unlike with AskBot “regular” users can’t close their own question. Closing topics is privileged operation for Trust Level 4 users, and AFAIK it’s currently not possible to grant that right to other TLs.