Oh man, in general, people be raving about aliens, but never give two looks to the ants in their garden. Or you know, the entirety of Australia. Or the deep sea. We have so much life that's alien buzzing around us. Hell, we even have the Scottish – humanoids that speak an entirely cryptic language. It's so much more compelling story-telling, too, if they don't arrive here in a spaceship, but rather have been living among us all this time.

I mean, not really? There's lots of reasons to use aliens in a story and I'm struggling to think of one that only works if you assume low-diversity planets