As you would imagine, we do not have the definitive answer. We just know that the financial markets are about nothing if not change. The market place has changed over the last decade or so. Primarily over the last five years or so. This isn't good and this isn't bad, it just is.
Extreme volatility is now a daily fact of life.
Maybe we can liken stocks to the bond world. In bonds, the longer a maturity, the more price volatility a bond experiences as interest rates change over short periods of time. Quite possibly that coupled with overvaluation is volatility's message to market participants. And now for something completely different. No more nudging.