However, even from the less cynical people, the question does arise from time to time. Why even bother writing fiction?
Themes are like the sun. If you look directly at them, you'll burn your eyes out. So you look to the side instead. You don't see the sun anymore but you still see the glow of its light. In a similar vein, it's like the mythology of ancient cultures. No one in Ancient Greece really understood why humans can be full of hate, greed, lust and envy, so they had the story of Pandora's box to explain it in a way they could understand. Furthermore, if you read, say, ten books about life on a deserted island, from Robinson Crusoe to Lord of the Flies, you're seeing that story in ten different ways because each author has a different interpretation to the subject material, and each interpretation illuminates something about the material that we didn't see before.
In regards to specific genres of fiction, we read them because of personal attraction. We read romance to remind ourselves that true love exists. We read horror for the thrill of a good scare, that fun jolt you get the first time you go to the Haunted Mansion at Disneyland. We read science fiction to understand the benefits and hazards of different sciences, as well as to see what our future may be like. Comedy makes us laugh. Erotica gets us off. Survivalism makes us raw and vulnerable.
In short, we read news and history and biography to stay informed; we read fiction to be entertained.