American reactions to 9/11

I was reading an article today in Wired magazine (this one) about a woman who had just become head of IARPA, a government agency tasked with outfitting US spies with advanced technology.

The part I found interesting was the reason she gave for switching from academic work to government work:

Like many Americans," she says, "I felt a need to step up and contribute."

It seems to me her thought process was "We were attacked, how can I help retaliate?". Now, she isn't unique in thinking like this as I've heard multiple stories of people joining the military after 9/11, but I do find it interesting that there weren't more Americans who didn't instead think "Why were we attacked?" or "What was it about us that made someone want to go to such lengths to inflict pain?"