Question about Public giveaways that are open for long periods of time.

I can understand Contributor giveaways being long as it gives more people who contribute a chance to win something, but why make a Public giveaway for a game like Magicka and leave it open for a month? Does it inflate the contributor's epeen when they see 4,000+ entries? Enlighten me wise SG members as I see no sense in this.