Likely, competitors, hostile investors, and/or NGOs are funding negative coverage through PR firms, just like Facebook itself recently did. (It happens more than you'd think.)

There's also a pile-on effect once a topic gets enough traction, and multiple outlets start publishing hit pieces in the hopes of gaining a few extra eyeballs.

Finally, government investigations into companies tend to create negative buzz, and since that's been happening with FB, that's probably generating some additional interest.

See also: Tesla.