Markets don't crash on bad news, they crash on good news. We get selloffs on bad news.
Here is an excerpt on the 87 crash: "A lot of work has been carried out to unravel the origin(s) of the crash, notably in the properties of trading and the structure of markets; however, no clear cause has been singled out. It is noteworthy that the strong market decline during October 1987 followed what for many countries had been an unprecedented market increase during the first nine months of the year and even before. In the U.S. market, for instance, stock prices advanced 31.4% over those nine months. Some commentators have suggested that the real cause of October's decline was that overinflated prices generated a speculative bubble during the earlier period."
Here is an excerpt on the 1929 crash: "The Roaring 20s--a time of growth and prosperity on Wall Street and Main Street--ended with the Great Crash of October 1929. The Great Depression that followed put 13 million Americans out of work. Two thousand investment firms went under, and the American banking industry underwent the biggest structural changes of its history, as a new era of government regulation began. Roosevelt's New Deal politics would follow. The October 1929 crash is a vivid illustration of several remarkable features often associated with crashes. First, stock market crashes are often unforeseen for most people, especially economists. "In a few months, I expect to see the stock market much higher than today." Those words were pronounced by Irving Fisher, America's distinguished and famous economist and professor of economics at Yale University, 14 days before Wall Street crashed on Black Tuesday, October 29, 1929. "A severe depression such as 1920-21 is outside the range of probability. We are not facing a protracted liquidation." This was the analysis offered days after the crash by the Harvard Economic Society to its subscribers. After continuous and erroneous optimistic forecasts, the society closed its doors in 1932. Thus, the two most renowned economic forecasting institutes in America at the time failed to predict that crash and depression were forthcoming and continued with their optimistic views, even as the Great Depression took hold of America.
The reason is simple: the prediction of trend-reversals constitutes by far the most difficult challenge posed to forecasters and is very unreliable, especially within the linear framework of standard (auto-regressive) economic models. A second general feature exemplified by the October 1929 event is that a financial collapse has never happened when things look bad. On the contrary, macroeconomic flows look good before crashes. Before every collapse, economists say the economy is in the best of all worlds. Everything looks rosy, stock markets go up and up, and macroeconomic flows (output, employment, etc.) appear to be improving further and further. This explains why a crash catches most people, especially economists, totally by surprise. The good times are invariably extrapolated linearly into the future. Is it not perceived as senseless by most people in a time of general euphoria to talk about crash and depression? The political mood before the October 1929 crash was also optimistic. In November 1928, Herbert Hoover was elected president of the United States in a landslide, and his election set off the greatest increase in stock buying to that date. Less than a year after the election, Wall Street crashed.