Is the friendliness of a neighborhood partly or more based on the net worth of the residents?

Boy; these neighbors keep to themselves! Fourteen months here and I’ve seen the next door neighbor twice! Directly across the street is a retired couple who I spoke to once when taking out my mail. I just decided to go, “Hi !” and she was friendly. She works a lot in her flowerbeds. Most of them pay $40 a week to have their yard mowed and edged. But when my kids were little and we lived in poorish neighborhoods I knew everybody. They came over; they wanted to talk. Our kids played together, we went shopping together. Here, I rarely lay eyes on anyone. What causes this difference in friendliness in different neighborhoods? I hear, “we used to know our neighbors.” Do you know your neighbors and, if not, why do you think that is the case? Note: I am not complaining about it; I’m just curious.