Maybe there's some truth to Douglas Adams' writing - we are just insignificant enough that nobody cares. In the Star Trek series it's similar, they are interested to see how pre-warp civilisations develop, seeing them as quaint, but that's it.

> Far out in the uncharted backwaters of the unfashionable end of the western spiral arm of the Galaxy lies a small unregarded yellow sun. Orbiting this at a distance of roughly ninety-two million miles is an utterly insignificant little blue green planet whose ape-descended life forms are so amazingly primitive that they still think digital watches are a pretty neat idea.