While Planets of Hats definitely do exist, this one is more excusable for me because I think that it would be possible for the distinctions between individuals of an alien culture to be overwhelmed for the characters by the sheer unfamiliarity of the culture as a whole. And as far as national-scale distinctions, the characters may not interact with a very diverse range of people from the planet, maybe they have one or two crew members being from there, or maybe they visit once specific site on the planet rather than traveling widely across it.
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