Hi Simon. While it’s easy to enable threaded replies, it would clash with overall Discussions UX logic. Just like Forums, they are meant to offer continuity by “bumping” the topic if there’s any reply - this encouraging the discussion to develop and create a more elaborate informative resource. If we thread replies, it would be hard to see where the latest one is in case it’s a reply to earlier posts. Posts with comments can be threaded, as they are meant to be more transient ,and comments are secondary. 

Hi Andrew, thanks for the explanation.