The Apple business model is based on marketing a carefully crafted user-experience founded on the tight integration of hardware and software. They are primarily

The Apple business model is based on marketing a carefully crafted user-experience founded on the tight integration of hardware and software. They are primarily a hardware company. Allowing their operating systems to run on arbitrary devices could result in less Apple hardware being sold. They learned the lesson from how IBM failed to maintain its 'walled garden' around the original IBM PC by neglecting to take ownership of DOS, which allowed their market to be swamped by PC clones, usually technically superior, all running DOS.