To avoid necro-posting—resurrecting closed topics that have exhausted their run, or renegotiating established decisions—this Discourse instance automatically closes topics after a variable number of days from the last reply; the number of days depends on the category, as some places see more “traffic” than others.
If you want to leave a comment to a topic that has been closed, you have the option of sending a message, via Discourse, to the admins or to the moderators; or, better yet, you can open a new topic, and link to the old, closed topics. Admins and moderators can merge topics at any point, and I can assure you all that we don’t pay per topic hosted on this instance, so there’s no reason whatsoever to shy away from creating new topics.