I recently discovered it but have noticed there has been little to no activity since mid to late 2019, and a few series are cut off. I was wondering why this cutoff happened and or what could be done to fix it.
At this point, I'm (technically) the guy who runs it.
Back when we started Universe Factory in 2015, we had a whole lot of activity - lots of interest, lots of authors, lost of posts. People gradually drifted away, in many cases from Worldbuilding Stack Exchange itself, something that was exacerbated by a network-wide crisis this past fall (see here for a bit of a timeline). Most of the most prolific authors have left over the last couple of years, and while we still get some submissions once in a blue moon, it feels a bit like a ghost ship. I've had an idea or two floating around for a bit, but I can't guarantee it'll become anything coherent anytime soon.
That said - we are open to new authors, new posts, and new ideas! Periodically, I've thought about putting together a meta post asking for new submissions, and if new users like yourself are aware of the blog - well, maybe there's enough interest. What I can say is that we would love to get new (and old) voices in. It's just a matter of figuring out how the heck we do that.