Because people are not made of money.
I can go see a movie with my wife for say..$15-20. That's about two hours of enjoyment. If I'm going to buy a game that is $60 and only get two or three hours of enjoyment out it I'm going to feel ripped off since. That's how I've always equated it. Now, if there is a lot of replay value, then I'm on board.
Now...if anyone wants to donate to the "Make Mightyduck filthy rich fund" I will gladly never complain about feeling ripped off again.
Pretty much this.
My argument is less about the absolute cost of the game and more about the fact that you pay that $20 regardless of the length of the movie. Whether or not a game should cost $60 is another subject, but my point is that regardless of what the price point of a game should be, why do we judge a game based on length and not a movie? I see your point that length can be more of an issue at $60 than at $15 but I guess I would be more upset if a game added padding to make it longer lowering my enjoyment of the game. Basically I'd rather play 2 hours of pure greatness and have that be the game than have to play through another 8 hours of mediocrity just because a studio felt the need to add more value to the game.