I have a theory that we love sci-fi so much because we love learning the rules of someone else's culture. It's the same reason that traveling is interesting. You get to set aside your own customs and habits for a while and get to know someone else's. What do they drink in the morning? What are their traffic laws? How do they say hello? What do they do on their birthdays? These are all fascinating questions, and the best sci-fi films scratch that itch for us. They drink Slurm in the morning, they drive flying cars, they say "live long and prosper," and they make a wish on candles that turn them 30 (Yes, I'm counting 13 Going On 30 as a sci-fi film).
We're curious people, and we love to discover things about each other. This is why we keep returning to our favorite sci-fi films. That, and because we love the memes about them.