Pirating whether you've downloaded a song,movie,games we have all done its on purpose knowing its wrong or on accident not knowing its illegal.
Reasons it cannot be stopped.
There are multiple pirating sites, for the government to try and stop the all would take forever and by the time they stop them all (if they could) hundreds would of already opened or reopened.
Sites as piratebay or others keep changing there ip's with software and changing there link address so its impossible to track them.
Reasons people that pirate don't get caught.
Millions of people downloads hundred of thousands is not millions of gig's of pirated data .
Imagine if they had to try and find each person they never would.
Conclusion
Pirating is probably the biggest trade in the world and the amount of sites there are and people downloading from them would be impossible to find ever one and track each site, and that's why pirating can never be stopped.