Mostly because it's entirely pointless, technologically. Netflix isn't even a particularly good source of digital video for piracy; the free-love internet video sharers are going to rip from the higher-res, sooner-available, better-library, non-DRMed commercial pirate versions.

The only people likely to rip video from Netflix are casual copiers, digital information hoarders, and people with legitimate compatibility/access issues.

It's kind of baffling that anyone making money off this business would want to drive these paying customers into the arms of Bittorrent, YouTube, etc.