
As Sastra mentioned, a lot of it has to do with cultural upbringing. If we stick to the canon lore for adventurers (that is, that we're not from around here anyway) it doesn't make a lot of sense to carry Eorzean biases with them. Anyone playing a native, though, is going to have grown up amidst the sometimes-fanatic racism and politicking that are prevalent in the society.
Of course, there's always going to be free thinkers who buck off that sort of mentality and just mesh with people they want to, but there is strong reinforcement to stick to your own kind: Ala Mhigan Highlanders tend to stick together as the collective outsiders on the continent, all stripes of Elezen have their own racial biases that make them all think they're superior and everyone else is below them, miqo'te of a tribal bent all believe that mating outside of the tribe/clan weakens them, etcetera.
I'm generalizing, of course, but there ARE racial tensions in Eorzea. Adventurers tend to not care as much, is all.
Of course, there's always going to be free thinkers who buck off that sort of mentality and just mesh with people they want to, but there is strong reinforcement to stick to your own kind: Ala Mhigan Highlanders tend to stick together as the collective outsiders on the continent, all stripes of Elezen have their own racial biases that make them all think they're superior and everyone else is below them, miqo'te of a tribal bent all believe that mating outside of the tribe/clan weakens them, etcetera.
I'm generalizing, of course, but there ARE racial tensions in Eorzea. Adventurers tend to not care as much, is all.