For the same reason a guy on the radio who says he even wrote a book about how his trading secrets made him $1.9 million in just a few short years wants you to sign up for his advice now.
Good stuff from Noah Smith, here:
If the writers of Zero Hedge really knew some information that could allow them to beat the market, why in God's name would they tell it to you? If they had half a brain, they'd just keep the info to themselves, trade on it, and make a profit! Maybe then, after they had made their profit, they'd release the news to the public (and collect ad revenue), but by then the news would be worthless. Financial news sites, you should realize, are not in the business of giving you insider tips out of the goodness of their hearts.