all they have to do is add more sugar to make up for the missing hazelnut
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For Nutella specifically, there are also differences in composition between the more wealthy European nations: https://www.youtube.com/watch?v=CXp2MTWNoZ4 According to that report, the texture is different to accommodate for the differences in common bread types, which makes a lot of sense IMO.
With how little actual hazelnut goes into a jar of Nutella compared to palm oil and sugar that make up most of the spread, I doubt Ferrero is saving a lot of money selling inferior product to poorer countries. With expensive goods such as meat and "pretty" vegetables, there's more money to be made.