| basically, no reason usually arises to bring that kind of thing to the fore (unless a story is specifically about the alien races' internal cultural differences), and there are lots of reasons not to bother with it (time, space if you're writing a book, budget if you're making a TV program or a film, and the general risk of confusing the reader/viewer with irrelevant detail), so it's not done, it's papered over with flimsy excuses, and we go on suspending our disbelief because things would be worse otherwise. :) |
