I spent 40 years in software development in the OS kernel area. Believe me, writing a new OS is not a trivial project. You need intimate knowledge of the hardware,for example, and do you think Apple is going to give you that? If you want to develop a new OS, fine, but how are you going to pay for it? You need to pay the people to do the work, equipment,testing, marketing, etc. What would be the return? You can't expect to sell it for a lot of money; most people are content with the Apple OS and are not likely to shell out money for a better OS. Granted enthusiasts would pay, but they tend not to spend a lot of money. And what do you do if Apple decides to make a hardware change that kills your OS? You couldn't expect Apple to keep their hardware the same just so your OS will work.