There is a pretty simpley answer on why US authorities are taking down sites like MegaUpload. And it is below. Sites like this have gone under the radar until they became too big and too successful for their own good. In order to survive and pay bandwidth and space costs, they needed to make money. And pretending they do not know the users they pay for the uploaded content are uploading pirated content was a good enough strategy so far. Not anymore.
One of the main reasons Kim Schmitz was indicted & arrested is the fact that megaupload’s records show they had a few dozen “high profile uploaders” on their payroll as a reward for uploading highly demanded copyrighted materials (one of the cases pointed out was one the X-Men movies).
The fact that the FBI & co. acted now was a just a clear message that they can deal with these issues without SOPA.