My mother, who was disabled by a stroke some years ago, relies on no non-medical technology as much as she relies on Facebook. It is how she keeps up with the family, who are scattered across the country (and, er, world), without which she would never get to talk to aunts/uncles/cousins since they see each other only at events/reunions and she often isn't well enough to travel.
I respect that folks don't find a lot of value in FB. It isn't quite my cup of tea either. But don't make the engineer's mistake of assuming "Since I don't use it, nobody uses it" or "Nobody's use of this is important to them."
Also, one shouldn't let one's position in the tech echo chamber cause one to overestimate how much resources Facebook really gets from society. Their annual operating budget is, what, the size of the school districts in one midsize US city or the IT department of a single large bank? Don't worry, we will still have brains to spare after someone does an A/B test on poking.