Intervention was not politically beneficial for anyone in the US government, while the invasions in the Middle East/bombings elsewhere etc. were. While people framed the invasions as humanitarian, if that were true, the Darfur situation was far more important and dire than the ones in the Middle East, though nobody wanted to help.
Unfortunatley, the United States failed Darfur and didn't provide enough support to the region. The tragedies that occurred in Darfur could have been avoided if we had taken a more proactive approach to preventing such tragedies. With that in mind, the U.S. should be severely reprimanded for its inaction today.
Yes, the U.S. should have done more for Darfur, because the situation was drastic. In Darfur, there was a great loss of human life, including non-militant women, children, and even men. The U.S. probably did not intervene because we do not have natural resource interests in the region. But it was a human tragedy that deserved our intervention.
Helping Darfur was not politically beneficial to the US, so there had been no reason to help the country - even though the Iraq issue was done, ostensibly, for moral reasons. While the moral case for helping the Iraqi people is sound, certainly, the same argument can be made for Darfur, there just wasn't enough to go around.
Although the genocide at Dafur was a tragedy, the US was not responsible for stopping it. The former colonial powers of Europe who cause the ethnic conflict in Africa should have intervened to stop the violence. The United States was not responsible for Darfur, and we were not required to do anything.