IMO, Facebook has been split into two groups 1) people aged 30 and older who can post and/or see pictures of their kids/grandchildren 2) People that are trying to impress their peers by posting pictures of their vacations/meals/fitness accomplishments,etc.
Facebook did a good job marketing and making a fairly user-friendly product that didn't "scare" older users. Unfortunately for them, that was also a good way to alienate them from the younger demographic.
To be fair, I think every social media platform will have a limited lifespan from here on out. Once the older demographic catches on to it, the younger generation is going to find something that is uniquely "theirs".