Well, I wouldn't say it's cuz they're black and they have no oil, but they are in Africa, and they have no strategic purpose for us. Same deal with Rawanda.
Also, while we haven't gone all G.I. Joe and nuked the janjaweed, our government has been pretty aggressive in this. Retiring US ambassador to the UN, Jon Danforth, has probably been the most vocal critic against what's going on there. Colin Powell, up until his last date in the State Department, was heavily involved in negotiations. Republicans and Democrats alike have been all over this in Congress, and a House committee (led by actor Don Cheadle apparently) just returned from Africa, confirming that while they did have that supposedly "historic" north/south peace compact, genocide is still going on in Darfur.
The word "genocide" also has a a lot to do with it, I think. The administration was very hesitant at first to call Darfur genocide, and with good cause perhaps. Sudan is the kind of area that once you go in there, you may never leave. Once you fight off the bad guys, then what? You still now have thousands of refugees who have had their villages destroyed and their livestock either killed or stolen. You're also surrounded by nations, not to sound parochial, that are filled with muslims that hate you. It would get played up as another "occupation," and it would thus give every ultra-leftist Chomsky snob in the country an excuse to sympathize with the next big jihad against America (sorry, had to get that in there
).
With all that said, despite the fears of a Somalia-like situation, I think that either the killings will stop, or we will send troops there ultimately. I think Bush's inaugural speech, with all the chatter of ending tyranny and "standing with oppressed peoples of the world" or whatever, it'll be hard to ignore their suffering.