Because they have no brains, but to make movies where shirts tear on their own and stupid lyrics come of out people's mouth making stupid dance moves. Have you seen Indian movies? Anyway, Indian people are more stupid then them, so they almost always elect celebrities when they might even have no interest in politics, e.g., Hema Malini.
PS: I am not insinuating that Hema Malini is stupid, only that she doesn't have much interest in Mathura or politics. I find that celebrities of previous generation were smarter and more sensible than celebrities of today.