It was a wasteland for a while but in my opinion has rebounded.
Otherwise...I don't get linkedin either. My gf used to work there and raved about it a lot but I still couldn't figure it out.
Before FB, it was possible to stay in contact with family, friends, etc. Was it as easy? Maybe. Email was perfectly fine. What FB (and everyone else in social too) was make so damn easy to post to the world "here's what I'm doing this exact second. please look at me!" The noise went sky high, and the signal went very faint. Then the algorithms kicked in, and the signal got even harder to find.
Does [increased polarisation of views] increase engagement? [Yes]
Therefore, we can conclude that Facebook does this.
FB is designed for maximum-engagement regardless of whether that is positive or negative for the useds (to use Richard Stallman's pun).