The market is several billion dollars and ripe for disruption. The revenue model, of course, is the billion dollar question. There are plans in the works, but nothing concrete and on the surface atm.
Because of the market perception of Facebook. People have been speculating about how much Facebook works and how they plan on making money in the future. If majority shareholders sell their shares as soon as they can, the share price goes down and everyone's nightmare comes true.
They could've maybe waited a little, for the sake of perception.