They seem closely aligned with the Free Software Foundation (FSF), so I could very well imagine that being a major ideological reason not to want to work with Apple. Yes, Apple sometimes upstream patches and they do contribute to open source here and there, but they certainly are no FSF poster child. Intel on the other hand are about as open as it gets when it comes to their track record in the graphics space. I personally have nothing but admiration for Rosenzweig's work and I hope they will continue to find environments where they can flourish and do great things in the years to come.