I thoroughly disagree with SinglenotSingle, who seems to be bitten by the bug that made Neville Chamberlain write off Czechoslovakia "a far off country of which we know little". The attitude is "We've done what we can, but if 50 women get beheaded out there, oh dear, oh well, but not our problem any more. We can't police the world."
I am a firm interventionist: I think we were right to get rid of the despots in Iraq and Afghanistan and I think we would be right to get rid of the despot in Syria, by warfare if needs be. The democracies of this world can and should police the world, and should eradicate tyrannies and dictatorships.
But the ignorance about the Yazidi does not come out of misogyny, it comes out of Western interest only lasting so long. I remember 10 years ago reading how Mugabe was the most vile despot and how he must go and indeed was on the verge of being toppled. That lasted about 3 months, and nothing happened, so the papers got bored. They picked up again when Mugabe was replaced by one of his cronies who promised something new but continued to rig elections and starve his people. The papers got bored so all our interest moved.
The plight of the Yazidi was a big topic a few years back, then the decent nations declined to do anything about it, so there was no new news story, so they went back to page 66.
Even today we have the despotic regime of Venezuela in the news but if that regime lasts out until, say, four weeks from now, the press will be bored of it and that regime's abuses, and revenge upon those who dared to challenge it, will just be ignored. (Ironically Trump and the media will have a symbiotic relationship here; if Trump gets bored and doesn't topple the Venezuelan regime, he'll forget about it and in turn the press will forget about it)
Public interest seems only to last as long as these stories garner interest in the media; start getting boring (eg via a stalemate), and they will be utterly forgotten.