It's gonna eventually come. Billion user services just don't pay for themselves. I don't say this to defend Facebook, because if even they sell it, the next person down the line will still be faced with the same monetization issues.
They were supposedly charging that, but the first year was free, and then every time you were close to running out of free time you would get x more free months. I chained those free months for years until it became completely free. So it was actually free to use.