> people are less naive about it and also realized they don't really care all that much about their second cousin's vacations or their old classmates' life updates

Young people do care - but the "checking on friends" and "showing off my glamourous life/vacation" has moved to Instagram and Snapchat. Partly because Facebook is full of "old people" and thus less cool. As the Insta generation starts to have their own kids, those kids indubitably will look for another platform...