x86 is protected by patents and only a few companies can use them, that’s why you don’t see random companies making x86 CPUs like they can with ARM (which also needs licensing but it’s much easier to get)
The first x86-64 processor has been released more than 20 years ago, so any patents on that base architecture (which includes SSE2) have already expired.
Good luck enforcing those software parents though in the current environment. My sense is that hardware companies put more faith in the enforceability of patent claims to something like CUDA than software companies with experience with litigating patent claims to APIs would. Post Oracle v. Google, something like CUDA is vulnerable to being knocked off.
And FWIW, that seems to be a reasonable result given the overall market structure at the moment. Having all eggs in the Nvidia basket is great for Nvidia shareholders, but not for customers and probably not even for the health of the surrounding industry.
genuine question, why don't these protections apply to emulators? How could emulators get away with emulating x86 but chip manufacturers cannot use x86 for their chips without a license?
Probably fair use, which is a subjective thing but one Intel must be confident enough they would lose. Or just lack of incentive, there is no money for Intel to gain if they win.