skeletonbow: They announced it as a 96hr promo IIRC, was it shorter than that? I never bothered to check to be honest.
moonshineshadow: As far as I know the Twitch stream was 96h and not the Insomnia promo, there was no definite end to it.
I just finished looking it up and you are indeed correct. The Insomnia announcement said that the promo would continue until "every single unit was sold", but nowhere do they mention how many units were to be offered up for sale either. I think everyone assumed there would be 3 complete rotations of the game lists because that is how past promos were done, and that was probably GOG's intention also, but they probably also had a limited time range to do the promo within agreements with publishers too, and the promo probably ran longer than they anticipated.
That's the nature of a sale like this that is unit-limited instead of time limited for given games, is that they can not predict how long a sale promo will last, meaning it could either end before they intend, or continue past their negotiated window of time which I suspect is what happened here.
I can't imagine GOG purposefully killing a promo like this ahead of time if they didn't have to anyway, it's either intentional to meet contractual obligations or a glitch in their system, either being equally plausible I imagine. I doubt there was any "hey guys, lets cut the promo off short and piss everyone off that was hoping for their game to come up, come on it'll be fun and we can all laugh in the cafeteria about it during lunch" going on. Seriously. :)