Subreddits and forums are fundamentally different.

Forums are linear and your are expected to have read all the post to post in one thread. There is also the old members who nag you into not creating a new thread but use the search tool to comment on an old one. There is forum local stars that control the discourse far more than on subreddits, and the photo + footer customization make them more prone starification and to group think.

On subreddit freshness is always welcomed even it is an old subject with a different spin. You are not expected to present you, there is no random subforum, you can be focused.