Earlier quoted context omitted.
OSX is much more than the kernel. Darwin is open source, even. What are you talking about?
How much of Apple's investment in OS X was in Darwin, and how much was in proprietary technology? Apple built a proprietary product using open source technology, and are now building proprietary products using open ML research. But it seems they're doing so for their own profit, not to benefit the open source and research communities.
You say it as its somehow contradictory. Open Source licences allow (LGPL etc), and some even welcome (BSD, MIT, Apache) creating proprietary software based on open source technologies.
Besides, Apple also did extend open source technologies (as open source) a hell of a lot. Webkit past Apple is 100x bigger/fancier/better than the puny KHTML it started from. Tons of LLVM work, especially all the early stuff, has been sponsored by Apple. Swift was made Open Source just recently...