Source? (you use them and don't disagree)
Well, I believe Facebook has said they have over a billion users, and if you add Instagram, Twitter, and Snapchat, I'm sure you are well over a billion. I personally use them, but don't necessarily disagree that they are useless and unnecessary. You're right, it may be that others agree, but still use them. Pure speculation, but I'd imagine out of a billion+ users (that's rounding down generously) I'm sure a large chunk of them disagree. Remember, these apps are what "run our world" these days.