That clause is really weird. IANAL (maybe it has specific meaning in law), but why is it even included as a clause rather than some comment / reminder saying that the licence doesn't make otherwise illegal things legal?
In practice nothing would change if they skipped it, right?
Not all jurisdictions forbid what that clause forbids, and even in some jurisdictions where it would normally be forbidden there may be circumstances under which you're permitted to do so, so it's definitely intended to forbid you from doing things that would otherwise be legal.
I'm also NAL, but circumvention is not always illegal, nor is running a legally purchased copy of OS X on non-apple hardware (or at least that was true when OS X was distributed on physical media, which is also when that clause was written).
It is likely in relation to running macOS on non apple hardware, as the Darwin kernel is often distributed with hackintosh tools. This would give them a reason to send a cease and desist otherwise legal software.
In practice nothing would change if they skipped it, right?