To your second point you might find some explanations in film studies. The rise of viscerally violent zombie/horror movies of the 2000s has been widely discussed. Its typically attributed to: political instability (911/war on terror); fear of diseases (2002 SARS/1999 west nile virus); natural disasters (Huricane Katrina 2005/climate change); and economic crisis (dotcom bubble 2000/2007 economic recession). Essentially widespread fears and anxieties shape our media and I think (some) video games being darker, grittier, and more violent in that time period reflect this.
To your second point you might find some explanations in film studies. The rise of viscerally violent zombie/horror movies of the 2000s has been widely discussed. Its typically attributed to: political instability (911/war on terror); fear of diseases (2002 SARS/1999 west nile virus); natural disasters (Huricane Katrina 2005/climate change); and economic crisis (dotcom bubble 2000/2007 economic recession). Essentially widespread fears and anxieties shape our media and I think (some) video games being darker, grittier, and more violent in that time period reflect this.