Because the people who back he IIPA are the same people behind the networks who stream everything for free to people within the US (via HULU etc), but decided it's not worth their time to try and secure advertisers in other countries, and put them all on a IP ban list. It shouldn't be a big surprise that when there are no legitimate avenues to obtain things, people would resort to piracy. But I doubt they actually care, because it gives them fodder to argue for tighter restrictions..