First off, let me thank Ziggurat Games for the great sale currently, where I was able to pick up some games, including a free one, at great prices, plus gift two free ones to a friend.

I have almost 20 games from Ziggurat Games now here at GOG and really appreciate them doing business with GOG.

However, they have many more games that simply aren't here ... not yet anyway ... and I don't know the reason(s) for that.

Maybe a year ago, I wrote to them asking about when WWII GI would turn up here, and my surprise that it didn't turn up when the companion game NAM did.

They kind of apologized and said they could give me no timeline about WWII GI, but it is their intent for all their games to be both available here and at Steam. I recently asked them again, and got no response ... I'd also asked them if it was DRM-Free at Steam.

Checking out Steam for WWII GI, I see that it has been available from them since about 2016.
Checking out Ziggurat Games, it appears they have only been around since some time in 2018.

There are quite a lot of games at Ziggurat Games that are what I consider quite good ones, that can be bought from Steam, including a bunch of hunting games.

When are those games, including WWII GI going to finally appear at GOG?

While we do occasionally get some good games here from Ziggurat Games, sometimes it seems like we get the dregs, rather than the really good stuff.

So who is at fault I wonder ... or what?

Is it down to special deals with Steam ... or is GOG curation holding them up?
Or is Ziggurat Games trying to milk them at Steam for as long as possible, just seeing GOG as a place to get a few extra sales when Steam sales drop off?
Or is it due to some prior licensing issue?

I'd sure like to have some idea of if or when those games are going to turn up here at GOG?

P.S. I've certainly seen WWII GI etc on sale at Steam a few times, and the same at the likes of IndieGala.

Yes, it was from another publisher. Retroism (with Nightdive Studios), maybe? I don't remember. Well, diferent tastes. I think GOG already has the best titles from Ziggurat (Legend, Accolade, Softdisk, New World). But I'm with you, we need all their catalog. I would buy their Ocean and Infogrames titles missing here and WWII as well. Just guessing some acts of their contract:
1. Ziggurat aproached GOG to release some old titles. At the same time, they took over games from other publishers already in the store (from Piko, Retroism and Majesco, as far as I remember).
2. GOG at first established which new titles they wanted (curation), to test waters.
3. During this testing time, they released NAM but hold off WWII, maybe to not clog that exactly "release window" with old shooters.
4. With a mature partnership, GOG gave green light for ALL Ziggurat games (if you search, you'll see that after some time Steam stopped getting exclusives).
5. But, by this time, GOG already had rejected some titles previously available elsewhere, and Ziggurat simply didn't care trying to renegociate so those games could come here. I suspect Ziggurat sales here must be very close to their sales at steam (Bloodrayne being an exception).

personally, I blame you

That makes no sense going by other series releases they have done here. NAM and WWII GI are a pigeon pair, that makes no sense to separate. I've not seen any evidence of that, and in fact I am only guessing that Steam exclusives may be the cause. And as has been mentioned by PixelBoy, there are a lot of games available from Ziggurat Games at Steam, that are not available at GOG, and many of those are much better in my opinion than many that have turned up here at GOG. I appreciate that Steam has a much larger customer base, and so there is a need to sell games there, but clearly something is stopping many of them from also being available at GOG, and for how long we simply don't know. Purely a guess on your part, and I see no reason for it to be the case, and it certainly doesn't match with what they told me about their end goal, of having all their games available here at GOG. Why would you suspect that? Steam have way more customers.
Without any facts to the contrary, logic alone would imply many more sales at Steam.
And there are other stores like IndieGala selling Steam Keys for games from Ziggurat Games. I would certainly consider buying some of them at Steam, if I was sure they were actually DRM-Free ... and a good price.

So I find it rather strange that my latest email to Ziggurat Games remains unanswered, as I made it kind of clear I would likely buy at Steam if they told me WWII GI was DRM-Free there, and if still no timeline for it turning up at GOG.

I just did a quick research and It's been almost a year steam don't get an exclusive from ziggurat. The last time was Hunting Unlimited 2003, released November/2020. Not an evidence, just a clue. Sure, it is, as I said so. 1. Ziggurat games get much more exposition on GOG store page and their marketing ads.
2. GOG customers are more inclined to buy old games.
3. GOG has less than 4000 games compared to the 50000 games on Steam. It's easier to discover less known games here.

I freely admit that I haven't chased up any dates, just gone by the number and type of games available from them at Steam, but not at GOG, so I am only claiming exclusivity deals as a possibility. The true answer is I don't know really, what the reason is. And I'm not denying it, just noting that it is indeed so. GOG can have as many banners etc as they like. What really matters is how many gamers see the marketing, and a lot more go to Steam than GOG, and Steam haven't been a slouch with promotional emails and I have seen a few sales of theirs promoting WWII GI etc. And it is not as if Steam don't have their own promotional banners ... just more of them no doubt.

And as I tried to say previously, it is not just about Steam themselves. I have seen at least two Ziggurat Sales at IndieGala that mentioned WWII GI. And they aren't the only store that does sales and sells Steam Keys, not by a long shot. That may have been the case many years ago, but Steam have plenty of old games now ... no doubt thanks to the early success of GOG. Perhaps. I'd certainly agree in some cases, but like I said above, numbers of customers (gamers) exposed to that is everything.

I would certainly hesitate to claim more gamers who love old games come to GOG. GOG's main claim to fame or focus, is DRM-Free, with old games coming second perhaps. Most gamers don't appear to give a rats about DRM-Free, and many like to buy all their games in one place if they can ... that being at Steam for most of them. Epic is of course trying to change that, but not sure that helps GOG any ... perhaps the opposite.

For many gamers, convenience is all, and while GOG is no longer niche, it is far removed from the behemoth of Steam and it's almost monopoly. There is always someone who wants to shoot the messenger. :P