FB has been a great way to not only maintain contact with people but to reunite with people I knew in childhood and adolescence that would have otherwise been lost to me. I don't spend much time in the app at all, but I appreciate being able to reach out or to offer emotional support (congratulations, condolences) in ways that would be impossible were I working my way through a phone book every month or so.
You might be interested to read an article⁰ where Sean Parker stated that they consciously designed Facebook to be addictive, by exploiting "dopamine-driven feedback loops".
⓪ - https://www.axios.com/sean-parker-facebook-was-designed-to-e...
For all we know, human groups have always used gossip as a way to bond. I guess these Facebook updates are addicting because they are a good implementation of something humans have always felt the need for.
It's sort of like watching the news - realistically a lot of news doesn't affect our day to day, but it's just interesting to see things happen. Like yesterday USA won the women's world cup. Did that have any impact on my life? Not at all, but it was nice to hear about. In that sense, Facebook is like a more personalized feed of news that always features people I at least used to know. It feels a bit like a mild addiction since it's not totally rational to care about these tiny updates in the lives of people I'm unlikely to ever meet again, but at this point I only check Facebook a couple times a week so I don't worry too much about it.