The news media is looking for new news, not old news. An ally killing someone in their embassy is new news; a regime of disrepute killing protestors is the same old story.

It's the same reason why election fraud in the US or Europe gets coverage when it's just a couple votes, but Russia's elections don't get much coverage. Everyone knows Russia's elections are a joke, but someone getting arrested for voting their deceased relative's ballot is unexpected.

It's not a measure of importance, it's a measure of newness.