That's not revenue. From Facebook's perspective, that's an input, a resource they have to obtain. Users are a supplier of raw material that Facebook distills &

That's not revenue. From Facebook's perspective, that's an input, a resource they have to obtain. Users are a supplier of raw material that Facebook distills & refines and sells on to the customers that pay them actual money. Like any business, they have to maintain a good relationship with their suppliers. In this case they have to provide a platform that users return to over & over again. But they optimize their business towards revenue generation, not suppliers.