You don't understand what a crash is. Crashes are caused by external factors, and because the market is based on speculation rather than actual growth, this factor, be it disease, drought, war, etc., these external factors cause the market to lean on itself, and when they do this without support, they collapse.
You're naive to think that a catastrophe isn't a predicable cause of a recession.
RE: Stock Market Implodes, Oil Prices Crash in Possible Global Recession