That Facebook makes money from mobile advertising is a good point: In the dot com era, many dot coms made money very briefly selling ads or services to other dot coms, who were willing to pay way too much. Now many companies are valuable because other companies will pay too much for user acquisition. If they stopped, their would be repercussions for a lot of companies in the middle (not Facebook) who see their business model go away.

If the base of the value chain isn't making money (and I think honestly in the current case even the middle isn't) the whole ecosystem will probably contract.