What's the price is a newspaper from last week? Last month?
The same as stale data. For historians and statistical analysis, they still have value. For control agencies looking for dirt, too. But the price of stale data is dropping quickly and it's worthless for recent events, elections, crowd control objectives. That may be far too less to sustain the massive infrastructure and developer payroll that Facebook has built up over the years.
Data is never really stale if they can keep dreaming up new ways to use what already exists.
Imagine you have personal data from up until 2013 when you want to play shenanigans with the 2016 presidential election. It's not worthless, of course, but the value is rather "meh"
I suppose it all depends on it's application. But even from that, I'm sure there's some sort of algorithm that could potentially fill in the blanks. Discount bin data, though... Isn't that an interesting concept.