BusinessInsider:

Because we’ve licensed so much other great content, Starz content is now down to about 8% of domestic Netflix subscribers’ viewing. As we add a huge more content in Q4, we expect Starz content to naturally drift down to 5-6% of domestic viewing in Q1. We are confident we can take the money we had earmarked for Starz renewal next year, and spend it with other content providers to maintain or even improve the Netflix experience.

Netflix CEO Reed Hastings notes that they have licensed more network and cable shows, as well as more first run movies from big studios. Maybe Starz just wasn’t worth the money to them anymore.