why do they do this?

I'm sorry that this happened.

I'm not gonna look at the specific cases or comment on them, but assuming the GAs were public - that would be an incentive for you to do group-only or invite-only GA's from now on.

I particularly felt burned in a few of my Publc GAs in the past and decided to gift only to certain groups, like PAGYWOSG. I now see my games frequently being played not long after being gifted. It shifts the whole situation.

I'm sure people can suggest other groups that could be good fits if you're looking for people actually enjoying your gifts. Sorry you had a few bad experiences

I don't trust lvl0-1 users o.O

some people will always break rules(generally the lower level users)

you can submit tickets for abuse of feedback system to get them forced to being marked as received(and likely users suspended), theres a reason alot of people mostly gift to groups/whitelist.... its to avoid these kinds of people and bots.

There will be always some abusers of course but you can create a ticket to force received mark. You have your proofs. There should be no problem.

As carenard says, you can submit a ticket with your screenshots and the feedback will be changed to received. I'm sorry for what happened to you.

Duro de gestionar cuando te toca lidiar con gente así, pero bueno los hay en todos lados.

Good job on gathering the proof about the games being on their library. At least it means they did activate the games and didn't sell them or something like that.
It's crazy that it even happened in the first place, considering that like 0.5% of the GAs every month are marked as not received. I think you just got very unlucky with winners. That's the optimistic way to see it.
I appreciate your philosophy of giving low levels a chance to win good games. Puzzles especially are a fair way to allow them to join, but sadly not a perfect measure. But close to, imo.

I prefer to do public giveaways only but it's stuff like this that causes some users to do group giveaways only. It sucks but that's probably the best way to avoid this happening again in the future, that or raise the level of your public giveaways. Sorry this happened to you but at least you have proof, so support should be able to change the feedback.

Yes, as others said, you can submit a ticket (one for each giveaway, btw), and solve it, and have again a clean slate. I hope you do good use of the "ignore" button.

But that only solves two specific cases, not the general issue. And, know what, that issue is unsolvable. Steamgifts users are people. And people can act right or wrong. There are multiaccounters with zillions of bots, autoentering scripts, no thanks, abusing the feedback system, a too-often found lack of respect for the giveaway maker's efforts and contributions. So it doesn't matter how many good users we have; the bad users make more noise. Much more noise.

So this hypothetical situation where you enter a bar, or a shop, or similar. There are let's say 20 customers currently in the premises. And one, note it's only one, is screaming and cussing and insulting without any apparent reason. So you could stand it and stay, or go somewhere else. Problem is, town is too small, so that's the only bar you like, the only shop that has several things you want to have on your normal life (plus one of the cashiers is your current crush). Now the decision is harder, because the option is stand the shit and stay, or go nowhere. No middle option. Not getting a cold beverage in a chill place with your kind of music after a hard day's work. Not getting many things you want or need. Because you can't stand even entering on those places anymore. Now that you've had to stand the idiot too often. You're so conscious of the idiot, that everything else disappears. And you wonder why the owners still let the idion in. Sometimes the customers make the idiot shut up for a while. But when you thought everything is going back to good, it starts again. You lose motivation and reasons to go. You can't even think of moving and changing town, because whatever hypothetical reason.

Now you're in the step of realizing how annoying the idiot can be, and how the idiot can ruin your time, your day, even after you've gone back home. And I feel you there. I've been for long on the edge of ragequitting and leave Steamgifts and Steam behind. Play games, but never a minute in SG, never a cent to Steam anymore. Seriously, for a long time, and often. There is one reason stopping me to do so; but I'm not going to even hint at it. You will find your own reason(s) to stay or leave, I guess just like every non-leecher, decent mannered person here in SG.

Remember you can always change your mind. Staying but ultimately deciding to go; or going, but returning some months/years later.

I'm sorry that happened to you. It's hard to see what they would gain by doing that. I wonder if it could be an accident (clicked the wrong button?). I suppose if the users have any posting activity on Steamgifts you could try asking them. But in general, thankfully such behavior is still a very small minority.