People don't necessarily have to be "on" Facebook for Facebook to collect data about their user. Many apps connect to Facebook. So they can collect data even when people are not using Facebook. The more people use Facebook connected services, the more data Facebook collects about users. Which means better ads for the users & better data for businesses.
Right, being "on" Facebook isn't a prereq for being under their umbrella.
Snapchat, Vine, and other networks are not under that umbrella, meaning it's still a zero sum game. These companies are competing for your attention, for which there is limited supply.
