Why should Facebook care? They should care because they need that content (obviously not individually, but in aggregate). There's an implicit agreement here -

Why should Facebook care? They should care because they need that content (obviously not individually, but in aggregate). There's an implicit agreement here - the user puts time and effort into providing content to Facebook that Facebook users want to see, and Facebook puts that content in front of lots of people. If the risk of Facebook reneging on the deal becomes seen as too high, fewer content creators are going to take up the offer.