Why is really important news swept under a rug?

I am talking about huge ecological disasters, the ones that make the news briefly then disappear, never to be heard of again. Oil spills are notorious for being ignored by the major news organizations. One of those huge container ships sinks every few days yet nothing is even mentioned about them.

Then you have that on going floating garbage patch in the Pacific Ocean that was mentioned a few years ago - well that thing has not disappeared. That was one disaster that could have been preveranted.

I often wonder if big business is not only controlling our government but also what we see and hear via the main stream media. I am so grateful that we have Twitter, where news is instant and almost viral.