I was just chatting about the “golden years” of Facebook with a friend today. I think it was about 10 years ago. Maybe we’re over-glamorizing the past, but at least the way we recall it: Around 2012-2014, the newsfeed mostly was just updates from your friends with some ads sprinkled in. Everyone was on Facebook, so if you were hosting a social event, you could just invite everyone on Facebook and they’d hear about it…
Facebook was essentially a way to connect to people outside your inner circle, and before 2012 it was a way for younger people to connect to other younger people outside school/college/university. It was similar to what Instagram does now except for the new friends feature.
Facebook works in a social environment where everyone knows your personal details and you maintain a casual-formal image (school, university...) but is useless in most other contexts. Instagram provides flexibility in who you can add, but is bad as a tool for socializing.