Facebook and Google was always about friends family and local before any random and stranger interaction becomes relevant.

Reddit and Lemmy is all about strangers. Oftentimes you dont even want people to know you or care about that. So userbase is way easier to create without feeling as if it was too small.

Facebook started locally and slowly created circles until the entire world found their friends and families and joined themselves

You were expecting Facebook, but google plus was always a creature more resembling Reddit and Lemmy. It was an aggregator, and source of discussion.