Honestly I am not as "negative", I don't really think the idea is to obsolete the Gog website in favor or a "Galaxy store" or even, as some seems to believe, it is a sign of Gog dropping DRM-free in favor of becoming just another key reseller. I think it's just Gog being Gog as in having a potentially good idea but with a bad implementation and an equally as bad communication.
I think all of that stem from them wanting to transform Galaxy into this big "universal client" not just for Gog game but for PC gaming platform and even console ones. In itself it's not a bad idea, multiple tentative have been done with limited level of success, but having somebody like CDPR behind it could definitely give it more traction.
But that's where Gog first mistake is IMHO, it's a good idea, but before you want to become an universal client maybe first try to be a fully featured client for your own store. While Galaxy is usable it's still rough around the edges, missing features that either the downloader or even the previous version of Galaxy had. Added to that, issues with offline installers being out of sync which, while IMHO being overblown, still exists from time to time and it contribute to peoples having the impression that Gog is wasting their resources.
Then apparently, on top of being the universal client for installing / launching game they apparently decided to also be some sort of store agnostic platform for purchasing games. I can see why they are doing it they want to show "gamers" that they don't try "lock" peoples onto a specific platform with Galaxy, that unlike Steam client, Epic client or others store clients with Galaxy you can chose which is your preferred store and purchase from it. Why not, it's still pretty funny that they chose Epic, mister "exclusive", as the first partner to display this feature but I guess Steam probably didn't give a damn about such a feature while Epic on the other side probably wanted to improve their image.
But again, IMHO, they screwed, again, the implementation, allowing other store on Galaxy is one thing, giving competitor some documented API that they can use to add their store to Galaxy is one thing, but handling the purchase yourself, with your return condition, curating the games available, and even handling support... I can see their reasoning, even if your purchase on another store through Galaxy you still have the same "guarantee" than you have while purchasing on Gog, that's nice, but not a good idea because... well this thread is part of the answer of why it's not a good idea... it muddle the water it makes you look like some standard key reseller (which I still don't think was their objective), I don't even think their main objective is really for it to be "profitable", more that they thought it was a good way to "promote" Galaxy.
So tl;dr I don't think it's some sort of apocalypse end of the world scenario where Gog will tomorrow stop selling DRM-Free game or become a second Humble Store selling mainly Steam/Epic keys and that you need to backup everything before they start putting Denuvo on Fallout 1 (it is still a good idea to have backup as a general rule though). I think it's was just a way they found to try to promote Galaxy as some sort of universal, store agnostic, client. But like always the implementation is not that great, the communication not really better, it blow up in their face and they don't really know how to disarm it (hence the silence treatment), not to mention that this time they probably have contract with Epic so it's not like they can pull back as easily as they did before.