Many more people died at the World Trade Center, the impact of the planes and subsequent collapse of the towers were more visually dramatic, and many people watched these things happen on live TV, or endlessly repeated on the news throughout that day.

The Pentagon was badly damaged, but not substantially destroyed, and the bulk of the original building remains. It was also not a "civilian" target, so its attack, while still generally considered deplorable, does not provoke the same level of outrage.