Why Facebook will never charge ...
... because it would render them liable to provide the service paid for on a contractual basis.
And one thing the legals systems of the world have been honed to do over the years, is regulate contract law.
It's one thing to offer a "premium" service which a few mugs will cough for (LinkedIn - if anyone does ???). But *every* *single* *user* ????? Imagine the sueballs then ?