I would agree with you, IF there weren't already a system in place to prevent that kind of grabbing of lots of game codes. There is a system in place though. The person doing the giveaway just removed those restrictions (which are turned on by default). So, the giveaway went exactly the way the person creating it set it to work.
The people doing giveaways can limit each user to exactly a max of 1 win per giveaway. They chose not to do that.
The winners used the giveaway exactly how it was made to work by the person doing the giveaway.
If the person doing the giveaway wants to give codes away that way, that's entirely up to them and it's kind of ridiculous to whine about it going down exactly the way it was intended.