I think you're also ignoring the influence of geography (or how countries apply and understand or perceive their geography) and humanitarian impulses (often fed by celebrities and the media). There's also the matter of different election cycles and basic national culture. Also, some nations don't intervene because they either don't need to or can count on someone else to do it for them.

The point about the media is interesting, but what "interesting stories" are you going to feed them? In addition to the desire to hold politicians accountable, I'd add the need to hold the media responsible for their actions. Sadly, this doesn't often happen (in either case).