The answer would be - it was not a country of interest.
The Rwandan genocide could have been easily avoided with the intervention of the global community, but it just didn't happened. There's multiple reasons and theories why there was not an intervention, but the most obvious one is that Rwanda was not a country of interest for neither the United States or the United Nations. Rwanda was not a country that could offer a lot to the US or UN, so the genocide was largely ignored and it took place without any problem for the committers of it.