The Star Trek world is based on a post scarcity economy, [which this article explains nicely][1].

My guess: because you are born in a place where all your basics are covered up until almost the top of [the pyramid][2], what is left is just [self-actualization][3]. What could be better for that than to explore the universe? I would sign blindly if I were there. Keep in mind that the Star Trek series only cover the intensive events: they won't cover an episode about a routine space exploration with no contact whatsoever, or we would fall asleep ;-).

I think they simply receive the feeling of having some meaningful stories in their lives + an awesome experience in the unknown! It's in us, otherwise why the **** did Columbus decide to get into so much trouble?


  [1]: https://medium.com/@RickWebb/the-economics-of-star-trek-29bab88d50
  [2]: http://en.wikipedia.org/wiki/Maslow%27s_hierarchy_of_needs
  [3]: http://en.wikipedia.org/wiki/Self-actualization