If we open our social media app for anything other than the express purpose of connecting with people, then we're opening it because we're bored. If we're bored, then what we fundamentally want is not to connect; we want to be entertained. We want something new. And at the point, the shift happens to incentivize the network to learn information about you and your interests, and leverage that information to show you things you might be interested in, and advertisers in turn leverage this to sell.