How come they don't have Gambling for TV and Movies?

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You can bet on sports and such, but not TV shows and films? I think it would be a cool way to gamble. Picture this, a show like The Sopranos, people would have been betting on who's gonna die, what's gonna happen before the season's over, etc. A movie like the next batman, they could bet on who the villain(s) will be. Or if it were Cloverfield, they could have gambled on which monster design was the closest one to the real one. How come they don't have this? Anyone else think its a great idea? Especially considering all the Film/TV rumours running rampant thanks to the internet, we could be gambling on which is the most legit. I like it because I like movies but hate sports.