The thing is, there WAS a military intervention in Rwanda.
It was called “Operation Turquoise“, carried out by the French government acting under a UN mandate, aimed at stabilising the recognised government of Rwanda and establishing a “safe zone”. It’s described in Conor’s book, and in most histories of the Rwandan genocide. It’s not at all an obscure fact about Rwanda that Operation Turquoise happened there.
The reason why humanitarian interventionists don’t typically mention Turquoise, however, is that it was an unmitigated disaster. It drew resources away from the existing UN peacekeeping force, it had confused rules of engagement which left it all too often acting as a bodyguard for genocidaires and it withdrew halfway through the genocide, leaving a massive refugee problem.
In other words, foreign intervention came with political goals that had very little to do with humanitarianism... as it usually does. Rwanda is an excellent example of why we should be wary of foreign intervention, and not one for interventionists to champion.