Why would people leave? Facebook knows your buttons and pushes them just right. In aggregate this is terrible for society, but individually it feels good.
Over the past year my view of Facebook has shifted from "I kinda don't like the privacy implications, but it is very useful for following what my extended family (most of whom live literally across the country) and friends are up to" to "why is this fucking thing sending me all these useless notifications all the time? (rhetorical question, I know why it is...) am I getting enough benefit out of it to be worth all of this or should I delete it?"
YMMV.