1) Detecting piracy is resource intensive. You have to design algorithms to detect infringement and you have to implement them in a way that can keep up with a respectable portion of your backbone bandwidth without significantly degrading performance for consumers.
2) File sharing protocols can adapt rapidly and will most likely make more and more extensive use of encryption. Distinguishing legal file sharing from illegal file sharing will only get more and more difficult. Even if there remain ways to detect infringement, this arms race with file-sharers will feed back into 1 in a big way.
3) As Neil Young famously put it, "Piracy is the new radio". Those who adapt to the "new radio" first will reap the rewards. Those who spend massive amounts of cash fighting the inevitable progress of technology will just fall behind.
What should these dinosaurs do if they want to stay competitive? Stop treating users of the "new radio" like criminals and win them over by providing a superior experience to what the pirates can deliver. e.g. Stop loading DVD's and bluray's up with annoying advertisements, anti-piracy messages, and warnings. Online stores shouldn't sell 720p videos or lossy music files when pirates are giving away 1080p videos and lossless audio for free. Above all, minimize the payment barrier. Make it cheap enough to feel like value is high and make it at least as easy and fast as pirating. In short, stop spending money to treat your customers like criminals and, instead, spend it to ensure that legal purchases are the path of least resistance to the highest quality experience.