This makes sense: online community is used to free stuff so that lowers down expectation of advertisers. The other reason: people contribute individually to Facebook but not deliberately for the network, more for their own desires for getting connected.
Facebook, as the filing declares repeatedly, has eight hundred and forty-five million M.A.U.s, or Monthly Active Users. (It has many fewer Maos, because it hasn’t yet figured out a way to get into China.) But it also only makes $3.7 billion in revenue. This means that it’s making a mere $4.39 off each user. Given how much time we spend on the site, it means Facebook is making just pennies an hour for each of us A.U.s.