I can't be sure, because I don't read anything they do since Dendrobates years ago, but my guess is that they're uploading here stuff (maybe not all of it) they're currently working on.
If I were to hazard a guess at a reason, it would be that they used to be one of the most prolific teams (perhaps they are, I had forgotten they existed when they didn't join MDex after Batoto's demise), with more than five thousand releases and hundreds of series. So they probably can't be bothered to upload all of that manually, and since they have a group-member-only upload policy, they won't want to relinquish that.
So whoever wants to read their old stuff will be able to do it at their reader. And perhaps even some of the current stuff, too, and the reason they put part of it here is to draw attention to their existence and have readers go to their place to check out the rest.
My guess is that it's an exercise in pointlessness, 'cause all of their stuff is to be found in Tachiyomi and Kissmanga anyway, and that's where the majority of readers will go. But who am I to dissipate castles in the sky?