It's a popularity contest. Most people are just going to vote for what they know and like.
Objectively I think that C2 wins against all of its opponents. I tried out Game Maker before (although it was GM 6), and my results were much worse than when found Construct Classic later. I don't really remember Kodu Game Lab, but it doesn't look like a boundless game engine, not even close. Scratch isn't even the same league as C2. And in my opinion game making engines are always greater than games.