This is another of those "debated areas" as far as I know. Section 8 of GPLv2 explicitly talks about geographical restrictions, and section 7 (IIRC) talks about complying with other regs & requirements. IIRC it's the view that "adding these restrictions to the license doesn't actually help" which has broader support, not "these restrictions are incompatible with <license>".
The FSF does argue strongly against them in the "free sw" introduction, but GPLv2 and others do include some explicit support for them.
I don't know the correct answer, just that if you ask three people you're definitely getting more than one answer (and there are only two possible

).
If you're asking why the initial release of code had this license, it's just because we could release a lot earlier with this license than with something else. Getting agreement that something less is safe and applicable takes longer, and we wanted the code out in public repos so other developers could work with it.
If you're asking "why does AMD have to follow US law" it's that "being headquartered in the US" thing AFAIK.