There is a large discrepancy between the recent economic numbers and the earnings reports thus far. Earnings are backward looking and if one waits for CEOs to tell them there is a slowdown than one will probably have already lost a lot of money. CEOs are notoriously over optimistic. As Warren Buffett says, he hasn't met a CEO that wasn't excited about their companies' prospects.
This does not mean that the short side is a slam dunk either. Hedge funds have largely de-risked which makes me wonder who the marginal seller will be. In addition, timing a market downturn is trickier than predicting one. In 2007 the market hit a high in October even though it was painfully obvious that the financial system was falling apart months before that.