Fundamentally speaking I reckon they know a bunch of fans will just pirate S4 now, and they reckon if you're into it enough to pirate it you'll come crawling back later. Doubt it'll kill their bottom line, but just a crappy way to treat the fanbase.
Trouble here is that people might get a taste for illegal downloads again after years of making it relatively easy to access stuff.
I've not torrented anything for years. I've been able to afford to support the things I like, and I'm perfectly happy to pay for content I want to watch.
It's pretty shitty that they've put fans in a position of either missing out, or exploring alternatives.