Why does the mass media ignore mass murder in Syria?

"One of the best indications this is the mainstream media's policy came this week when the Syrian government and the Syrian opposition traded accusations over who was using poison gas again in Syria. This should be a big news story for the mainstream media but it has raised hardly a murmur. 
The media paid attention to Syria as never before after the 21 August sarin attack because it involved Obama's called bluff and it showed the bodies as never before. As if a hundred thousand people had not been slaughtered already by non-chemical means, the media jumped all over the chemical attack as though it was a fetish. The shameless pro-Assad forces in the blogosphere took up the defense of Assad as if proving he didn't do the sarin attack was the same as exonerating him of mass murder. Even while the media failed to report on Assad's continuing siege of Ghouta, using both bombardment and starvation as weapons, they gave coverage for everybody's opinions and findings on the chemical attack.
There can be little doubt that there have been new chemical attacks in Syria, since both sides agree there have been. While they both predictively point the finger at get other, if the reports that the gas bombs there dropped out of helicopters are accurate, there can be little doubt that those were Assad regime helicopters. Given the history of coverage on the chemical question in Syria, one would expect reports of a new chemical attack to break through this news blackout.
Why hasn't it?"