This explains a lot. About 2 years ago my feed suddenly began to be filled with posts from random pages I had followed. Some I had followed a decade ago and had not seen a post from in years. BTW, when I say filled I mean filled. Literally like 30 page posts with maybe one IRL friend or family post showing up in-between.
It got so bad that to actually see the family photos and announcements I cared about I had to manually unsubscribe from almost every page I had ever followed. I guess I'll never know for sure but I'm going to guess "boosting" was to blame?