If you don't 'effing' care maybe you should eff off and leave people to do as they please.
Fb is not mandatory, moaning about it is boring. Who knows what's really going on for some of these people, they may crave interaction/validity and just have no one to talk to. Fb lets them reach out in a way that suits them.
I don't use fb much but when I was in the depths of despair and too anxious and depressed to ask for help I really thrived on just the sort of stuff that you probably hate. It helped me, it might be helping others too.
And actually there are plenty of threads on mn where people discuss what they had for dinner, what their pets do and how tired/stressed/skint they are.