Comment by rossdavidh

Exactly, and unlike, say, Google or Apple, I don't think Facebook has really ever had more than one big payoff idea. If that core business model/idea has seen most of its growth, and may even decline, then there is really not much reason to expect it to find any other way to keep growing. They are big, they are profitable, but they are not going to be growing fast in the future, and one could argue should be valued (in terms of earnings/share) more like a utility or a consumer commodity manufacturer, than a technology firm.