Depending on how accurate Sternheimers figures are, that clearly didn't happen. We're not ignorant to the fact that mass media holds a powerful influence on consumers (for better or for worse). But the archaic belief that video games encourage mass killing rather than merely galvanizing an already unstable individual in the minority is just flawed. The number of people playing games is up as crime rates continue to decline. The correlation isn't there.
So why is it so popular to blame games? Hit the read link for an interesting take (in PDF). The short answer; you blame what you don't understand.