Generally that is down to lazy writing, you see it in fantasy as well, all elves, all vulcans, all dwarves are all the same because it is easier to just write them that way. An in universe explanation would be that since the media is generally presented from a human centric perspective that they don't recognize the differences between say a high elf and a wood elf while it would be instantly recognizable to any elf those differences. Which is actually very realistic when you have one ethnicity looking at other cultural groups and not seeing the difference between similar subsets in those groups.

Generally that is down to lazy writing, you see it in fantasy as well, all elves, all vulcana, all dwarves are all the same because it is easier to just write them that way. An in universe explanation would be that since the media is generally presented from a human centric perspective that they don't recognize the differences between say a high elf and a wood elf while it would be instantly recognizable to any elf those differences. Which is actually very realistic when you have one ethnicity looking at other cultural groups and not seeing the difference between similar subsets in those groups.