How do you know that +10% is after the bottom and not a temporary bump on the way down?
Most investors set stop loss levels for themselves. So when a stock crashes through those levels it triggers a lot of sell orders which makes the stock go down more triggering more stop losses, etc. Once the cascade has stopped, the game changes a little bit and fundamentals are reconsidered.
[Edit] And I didn't mean a 10% bounce immediately after the fall, but rather a gradual move up over the course of a few weeks.