You don't understand: this is already done by social networks, behind the scenes. You just don't get to set those thresholds. They make money by tweaking those

You don't understand: this is already done by social networks, behind the scenes. You just don't get to set those thresholds. They make money by tweaking those thresholds so that you'll be interested in what their paying customers (advertisers) actually want you to be interested in. Giving you back the power to change that, would be the end of their business model.