I have no idea if it's new or if it's a bug, but I do think Microsoft is now on the company list :
https://www.gog.com/games?devpub=microsoft It's difficult to don't make the connection with this :
|Xbox Wire] Our Approach to PC Gaming "
More Choice in Where to Buy Xbox Game Studios Titles"
"With that in mind, our intent is to make our Xbox Game Studios PC games available in multiple stores, including our own Microsoft Store on Windows, at their launch. We believe you should have choice in where you buy your PC games."
"In March, we announced that Halo: The Master Chief Collection will come to PC later this year, launching on Steam in addition to the Microsoft Store on Windows. We will continue to add to the more than 20 Xbox Game Studios titles on Steam, starting with Gears 5 and all Age of Empires I, II & III: Definitive Editions. [...] We also know that there are other stores on PC, and we are working to enable more choice in which store you can find our Xbox Game Studios titles in the future."