Humans like stories because we look for the world around us to fit into a narrative -- the rags-to-riches tale, the sports underdog overcoming the odds, the karaoke hustler singing a song about sex with his daughter, etc. You saw this happen immediately with Brad Pitt and Angelina Jolie's breakup. The original reason reported for their divorce was Pitt having an affair with his recent co-star Marion Cotillard. What goes around comes around, Angie! Once a cheater, always a cheater! People knew how to deal with that version of the story; it was nice and simple and fit into a form that we are all familiar with. When it turned out to have nothing to do with cheating and became much more complicated (like all divorces), people lost interest.
We moved on to the other 35 percent of topics: dreams we had, food we ate, and bowel movements we took.
While it might seem like this fixation is born of our fame-obsessed time, in reality, it's been around since we climbed down from the trees. In the past, we had gods and heroes filling this role. Think of the Greek deities, whose sexual exploits alone would fill a thousand tabloids. Then it was royals, military heroes, and explorers. Film stars and musicians showed up around the beginning of the 20th Century, and are merely the latest group filling this need. Who knows, your grandkids might get their rocks off gossiping about the Queen of Mars releasing a diss track about "those space station pussies."