why do people enter for games they already have?

GREED:)

Sometimes that happens because the person entered a lot of giveaways for a game they wanted and won the game, but forgot to remove the other entries.

Aside from that, I have no idea.

A couple of weeks ago I won a bundle game which I bought meanwhile, but I didn't remove my entries. The gifter sent me the key via mail, but I asked him to reroll because I already own the game now and I won't use his key. Maybe your winners where in the same situation?

May I ask what game it was ?

There's nothing wrong with having a game in your inventory and then winning the same game? And you can't enter a giveaway if you already have the game?

I had a game re-rolled once but the guy already owned it.
So I requested antoher re-roll, but even that guy already owned it.
So I requested a third re-roll.......and it selected the first guy again -_-

Oh, Ive made 8 rerolls on Sniper: Ghost Warrior DLC. After many rerolls, support and me agreed to delete that giveaway.

Because they're assholes.