I don't know if it's the reason, but I understand that a lot of market-moving news is released after close so that participants have time to digest it and decid

I don't know if it's the reason, but I understand that a lot of market-moving news is released after close so that participants have time to digest it and decide whether their positions still make sense. The next day's opening auction will deal with the increased volatility better (see the story about the NYSE "forgetting" to hold the opening auction and the resulting chaos)