Social Media is much more than clicking and reading. It is about how many ads that go before the eyes of readers. Those who are most active on Social Media tend to be more pliable in their political views based on their lack of real world experience. (They spend more time in front of screens than their cohorts that are busy doing other things) They are also more readily available to watch the ads and buy the products that are just a click away.
A social media company attracts the advertisers that cater to this audience by keeping them clicking on those pages that make them feel that they are smart. More page views, more sales, more ads. So, catering to people who exist on the fringes of the day to day world in their online bubbles is good business. Rumors, Conspiracy Theories, and outright lies are much more believable for someone who has little interaction with the rest of the world. Unfortunately, many in the Mass Media and Political circles believe that Twitter and Facebook reflect the perceptions of many more people than they actually do.