While that is true, they also create their own little closed ecosystems that a new member, or even an established community member, could easily overlook entirely. If I'm a newbie scrolling through the forum index, how is a folder named "Blue Planet" or "Wings of Dawn" going to jump out at me in any way without external prodding? Unless I happen to see some sort of external post or highlight, I'll never think to look there. Or as a personal example, I (very ashamedly) haven't yet played either WoD or the latest portion of BP, so I pretty much avoid those folders entirely for the sake of not being spoiled by a bunch of people talking about things I haven't experienced yet. (Plus the War in Heaven discussion thread is an over 250-page threadnaught that's essentially impenetrable to new readers.) As a result I know I've missed out on learning about really cool new features that both of your projects have introduced. The Unread Posts listing isn't a great answer either, since then you're getting a huge unsorted list of everything that goes on, so a bunch of threads are going to slip through the cracks there too. (It's also incompatible with how I tend to browse forums myself, but that's beside the point.)
Honestly, if we do need to keep the hosted folders (or at least a few of the more active ones), I would still highly suggest that we keep the idea of an All Releases folder that's a home for everything the community produces, coupled with a tagging mod to make it easy to sort by category. And even if your project has its own individual folder, you'd still be highly encouraged to post a thread there if you released new content. Even if it's a locked thread with a single-line blurb and a redirect to your own folder's thread, at least it means that someone can conceivably just follow that one folder and still keep on top of everything that's going on. Think of it like a Highlights folder, only open to every content creator to post.