Because there is no variation in I.Q, from country to country across the globe - just like there is absolutely no variation in average height, melanin content of the skin, etc. from country to country.
People in, e.g., Somalia have, on the whole, the same average I.Q. (= 100) as people in, say, Norway - just as there is no noticeable difference in skull shape, eye color, or hair structure between the two populations. Indeed, they are the same for all human populations, without exception.
It is not possible to distinguish, with the naked eye, an Australian Aborigine from an Eskimo, nor a Scotsman from a Tamil. Nor would the large-scale I.Q. testing of different populations reveal any discrepancies.
We are all alike - in every respect.
Regards,
IQ is pseudo-science dating back to an era when the likes of Edgar Cayce and the Maria Orsich were inspirations for the likes of Heinrich Himmler.
The only reason the neo-nazis still get away with bs graphs like the one posted is because a wealthy cadre of eugenisists prop then up with funding for junk “research” such as the Bell Curve book.