Lets assume for a second that Facebook's only goal is to maximise global scrolling, (measured in metres, say). They obviously need content for people to scroll

Lets assume for a second that Facebook's only goal is to maximise global scrolling, (measured in metres, say). They obviously need content for people to scroll through. If I post something compelling, potentially all my friends will scroll an extra 20cm. If I have 300 friends, that's a total of 60 metres extra scrolling in the world. More than I alone am likely to scroll in a day.