One factor: it provides variable interval positive reinforcement* - those moments when you see a page which describes something you recognize happening all the time, and those moments when you see a show you recognize acknowledged on the page.

* Edit for those who don't want to follow the link: variable-interval reinforcement occurs with some set frequency (approximately, in this case), but at non-equal spacings. Other things with variable intervals are raindrops falling on a small area of pavement, cars passing on a street, and other things which are loosely modeled by Poisson processes. Any (say) ten-minute period has about the same number as any other ten-minute period, but they aren't spread out at regular intervals.