JanusVR is interesting, but yes, like you say it is a ghost town. To me it seems more like a kind of strange museum cataloguing digital artifacts that may not really need to be remembered. The ease of use is there, I was able to get a space of my own up and running on my local machine and I'm an amateur at best when it comes to coding. I think the fatal flaw is that it lacks an incentive for people to be there. The cool factor wears off pretty quickly when there's nothing more to do than explore empty half baked concepts with little to no interactivity.
I personally think that 3D VR spaces like this would benefit by being tied to a blockchain that rewards users and developers alike, like Steem. But I haven't put a ton of thought into it and someone smarter than me could probably figure out why it's a bad idea... Or it could be a great idea that really kickstarts the 3D web and gets the metaverse rolling!