The problem is that they are trying to hyper-monetize. Zuckerberg turned down a $2BN offer from Yahoo, so clearly he believed he could make the company worth more than that.
Zuckerberg is actually proving that they're worth more, the way in which he goes about it is not the most elegant though. I'm still willing to bet he'll succeed but the image of facebook is tarnished for ever, and it could very well be that if he does manage to sell for a much higher valuation that the buyer will find themselves with another broadcast.com.
Facebook is very dependent on being a single entity. If it sells, it has to sell to a company larger than itself, and that's about the only thing scarier from a user standpoint than what Facebook has already done.
I thought that Yahoo offered $1B and Microsoft (later) offered several (15?) billion.
Note that Zuckerberg may have interests other than money. For example, he may be happier running a company worth $3B than having $5B.
But Ballmer had come with something more sweeping in mind. "Why don't we just buy you for $15 billion?" he replied, according to a very knowledgeable source. Zuckerberg was unmoved even by this offer. "I don't want to sell the company unless I can keep control," said Zuckerberg, as he always did in such situations. Ballmer took this reply as a sort of challenge. He went back to Microsoft's headquarters and concocted a plan intended to acquire Facebook in stages over a period of years to enable Zuckerberg to keep calling the shots.
Zuckerberg also rejected that offer. The deal that was struck was for $250M at a $15B valuation