Thanks for the info! At first thought, seems there's no reason to keep this listing, but it looks like the complete version of the game is <Bundle>-typed on Steam, which means it can't be listed on SG. Staff may be intentionally keeping the current listing for that reason, but I'll run it by them to see (and it's not like you can't also just list under any of the other individual episodes, which would at least give some CV) .

losing something free cannot be considered a waste,

Okay, putting aside the countless other examples of why that's completely unsupportable, let's go straight to snark:
You didn't pay anything to be born, right? So presumably, by the given logic, you (or anyone else) dying would not be a waste?
[To be clear, this isn't meant as hostility, but to highlight the issue with the statement in question.]

Resources have worth (inherent) and value (subjective) regardless of how they're acquired. Value may change, depending on worth or demand, but the acquisition itself never affects the value or worth [barring effects to value due to broader social considerations, as with blood diamonds; But technically that relates to the presentation of the item, rather than its own value; Repackage the diamond and you're fine again]. Well, the person acquiring it could value it less because it's free, but that'd just be proof that the individual is profoundly irrational. Doesn't really say much about the item itself.

In any case, the key may potentially allow for the game to drop cards (I can't find a thread on SG for the GMG freebie to confirm), so this may have quite a lot of appeal to a given individual. Nevermind that if it does drop cards, it'd be non-ratio-affecting free wallet funds, at worst. That's pretty favorable for a giveaway that costs nothing to enter. So even without factoring in "waste" on the gifter's end, we can still determine there's potential "not-waste" on the receiving end. Meaning it'd still, ultimately, be a waste to simply dispose of the key.

Finally, going off site rules, it's best not to bother a user for their general site usage or to target them with hostility (though this is more towards Ognarisog's comment than your own). This is especially true when it comes to comments which may discourage gifting, as staff is especially strict on such. If there's an argument with the site structure- say, it allowing for free games to be listed in the giveaway list- it's far better (and far more reasonable) to take it up with staff in a support ticket.

Rather, I don't actually believe perma-free games are supposed to be listed in the giveaway list, so there may be reasonable cause to mention this specific title to staff. In the meantime, the GA creator here is just going along with what the site allows, with no ill intentions and no exploitation (intentional or accidental) in effect [unless one believes they're doing this just for a +1 to their giveaway count? But that's so minor, I can't imagine caring about the matter enough to pay it any mind]. There's just no reason to directly take them on over the matter.