I appreciate the OP's bewilderment, I do. A similar thing happened to me some years ago: I had posted a question which attracted a fair number of comments, the comments were nearly all on-topic and I thought really useful for anyone intrigued by my question. But the list of comments continued to grow until a moderator transferred all of them to chat.
When I ...
The chat room was deleted automatically for lack of activity. I'm a little surprised that that happens.
It's been undeleted, since that's possible, but there's no guarantee it won't disappear again. Comments are ephemeral.