“But wait, what about regional differences within countries?”
Yes, indeed, there are huge differences!
Northern Germany vs. Bavaria. Cologne vs. Eifel. Saxony is not Schwarzwald. New York City vs. Mobile, Alabama. Georgia is not Oregon. San Francisco vs. Nashville.
And those differences are especially relevant when you throw people from different regions within a country together into one company.
But, when you throw people from different countries together, the regional differences within the respective countries become far less relevant. The focus then becomes on the differences between the countries.