I experienced the exact same thing as I got into my 30s, as well as a huge increase in posts appearing in my newsfeed just because a friend 'liked' it. So I'm s

I experienced the exact same thing as I got into my 30s, as well as a huge increase in posts appearing in my newsfeed just because a friend 'liked' it. So I'm suddenly seeing the wedding and baby photos of people I've never even met. It just felt creepy and weird, like I was intruding on people's private moments. I think this is because, as you say, people maintain radio silence apart from major life events. When someone posts one of these major events, everyone else feels like they have to hit 'like' out of a sense of loyalty, which propagates these posts much further across the graph. These are the only type of posts I've seen that routinely get 100+ likes. I actually think this could be a factor in the downfall of FB, as it develops its own social norms (e.g. "I must always 'like' any photo of a female hand with an engagement ring on it, despite the fact it looks identical to every other one"). The number of likes a post receives is now completely divorced (pun intended) from the inherent quality of the post, so the like button no longer works as an upvote system.