I understand why you might jump to that conclusion. However, keep in mind that we have a Developer mode where you can do whatever you want including using your own kernel. Aside from the aspect that I personally think anyone should be able to do whatever they want with their own hardware, it makes sense from a security perspective. Just look at the console market. Consoles that allowed alternative operating systems took much of the incentive out of hacking the security subsystem of those consoles.