Why is it so hard to create a good science fiction movie romance?

Some of the coolest science fiction movies of all time are love storiesEternal Sunshine, Brazil, and plenty of others. Combining big ideas with an epic passion just makes sense. But why do so many films fail to pull off this combination? Watching the new movie Upside Down, which fails so spectacularly as a love… » 3/15/13 9:00am 3/15/13 9:00am