I think there are a few factors. The other side never tires, and it always offers something new. This novelty is different to a conversation with a real (or vi

I think there are a few factors. The other side never tires, and it always offers something new. This novelty is different to a conversation with a real (or virtual) human that will tire or run out of new content which leads to natural boredom. The effort is also smaller. Bite size interactions are easy to digest and "just one more" whereas starting a new movie or TV show has a larger mental hurdle. It also has elements of gambling. What's in the news feed mystery box this time? Refresh and see. It does not have to be good every time. Intermittent reinforcement takes care of that. In this respect it has a lot in common with many video games.