I think you may be overestimating how effective the international community is at stopping genocide. The allies were shocked when they liberated the death camps because they simply weren't aware of it. And even if you have the modern era, plenty of remote places either don't have good contact with the developed world, or simply are too poor and difficult for the UN Security Council to bother with. UN intervention against genocide is the exception rather than the rule. That said, if it's known, there will probably be sanctions of some sort. But that's not to say they will hurt the perpetrators.
Guatemala, Bangladesh, Burundi, Cambodia, Iraq, Rwanda, Sbrenica, Sudan, Iraq again. Not to mention other historical genocides which are less known, for instance the Holodomor by Russians against Ukranians, the genocide against Armenians, and a separate one against Greeks, by Turks. It's all very depressing, frankly. Because it happens and the vast majority of people do get away with it.
The sad reality is simply that it takes a lot for the world's major powers to give a shit. China's foreign policy is aggressively non-interventionist, and the USA and Russia just aren't bothered. The NATO intervention in the Balkans was pretty unusual, probably because it was too close to home. But if it happens in Africa or Asia? Or if the nation doing it is too big of a deal to take down (has atomic weapons for instance), it can do as it likes to its own people.
And if the genocide, or anything like it, would be helpful to get rid of people who are generally on the other side of your sphere of influence? Fabulous. Operation Condor for instance was a cold war operation by Latin Americas right-wing dictatorships to get rid of leftist elements in their populations. Tens of thousands of people went "missing". Henry Kissinger, America's then Secretary of State, told Chile's government that the human rights conference they were hosting in the region "didn't apply" to them, and that they didn't need to worry about whatever operations they did overseas. A few days after saying that a car bomb killed a prominent Chilean human rights lawyer in Washington D.C. but they were allies against communism, so who cares, right? Even if the world's TV cameras and smartphones are aimed right at the bloody events, that's no guarantee anything will be done. And even if something is done, that's not to say it will be of much use (Syria?)