JakobFel: I think the main reason it's not on GOG at this point is the Bethesda.net integration. Skyrim: Special Edition in 2016 added a full integration with Bethesda.net, both for mods and for Creation Club. While I assume it's possible for Bethesda to make that part optional (probably only for Galaxy users), I don't think it'd go down well here. As for the game before the remaster, Bethesda isn't actively selling that on Steam so it likely wouldn't be something they'd be willing to do on GOG either.
It's a shame, too, because I'd absolutely re-buy both Skyrim and Fallout 4 over here if only they were here.
Exactly.
Likely, when coming to GOG, Bethesda would have to remove or disable ALL of the Bethesda.Net and Paid-Mod integration.
That's if they'll even bring that here now...and I'll get into some thoughts on that at the end of this post.
And I think more games w/ these type of integrations and while being active w/ still getting DLC's, updates, patches, expansions, etc - yeah, they ain't going to be coming to GOG until much later, when Bethesda feels like a run of DLC, Expansions, NBonuses, Paid Mods, Bethesda.Net Integration, and/or other junk is totally done w/ - and then they might just bring it to GOG without any of the other version's non-sense.
That way, when the game's run is Complete and all of the content's compiled for a GOG release - they don't have to keep updating the game and getting its new contents approved by GOG every time; they can just bring it to GOG in one big swoop and be done w/ it.
Worth pointing out here to add more to my above-said point - when coming to GOG...Morrowind, Oblivion, Fallout New Vegas, Fallout 3, Prey 2017, The Evil Within 1, and all Dishonored games actually ALL came here in basically a final and Complete Edition state (with ALL DLC's and expansions).
There's also now that Microsoft owns Bethesda - and it's also possible since there's no real deal w/ GOG and Microsoft here for their games on this store and since Microsoft is pushing Game Pass on PC and consoles so hard, it might not even come here anytime soon or even at all.