I agree to some level like I noticed the activity is down in the forums but I think OP pretty much hit the mark on weeding out who truly wants the game, canceling out side-liners, and discouraging leechers. I'm monitoring this thread for ideas when I do a giveaway in the future.
The forum activity has been low for a while, i think that it's only getting worst because people are getting tired of what's happening lately to the forum, it's the human garbage that has been plaguing the forum (due to popularity of the website and the endless dump of keys from bundles), it's the "add friend" threads that is getting repetitive/annoying, the lack of effort in some posts (ex. In a thread like "Games finished in 2015" people drive by with posts like "Yeah, i played Super Mario, he jumped and it was cool"... That's not adding nothing to a conversation.), it's the changes that no one asked for and only brings more problems, etc.
This is a small community, if people keep leaving and there's a low number of people joining (and i'm not talking about the folks that just bought TW3) it's obvious that is the result. Gog just doesn't know how to cater their community, it keeps ignoring it because they know the majority of their customers don't even come here.
But back to the giveaway, it's a bit of both, most of the deserving people already has the game or isn't interested and the other people, like you said, can't participate because i don't allow it.
There was more people interesting in Stalker Clear Sky (the worst of the franchise and that was given away many times) than people participating on this giveaway, if i was to make another giveaway with the same game but without my "barrier" there would be 3 or 4 times more of participants.
Edit- Also considering just giving the code(s) to Sachys.
I respect Sachys decisions (and agree to some extend) but his solution is far from perfect, especially when it punishes good members. But it's his call as it should be your call, your decision to do whatever you want with your keys, the only thing that you have to keep in mind is that in your act of good will you can also be "hurting" the forum by continuing this cycle of leechers/keys dump.
BTW, is it just me who thinks that the latest store promotions lack any impact?
In what way? I think it has been up to par with the usual weekly/weekend sales unless you're confusing the whole TotalBiscuit weekend with a major sale (ex. Insomnia sales or Summer sale).