Why is it that you never coincidentally bump into any friends and classmates whom you grew up with in school, even though you still live in the same town?

I graduated from high school 35 years ago in a small suburban town. My graduating class size was just over 500 people. Ever since high school graduation, bumping into anyone by chance has been rare. I know at least 65% of my class still live here today or at least their family (e.g., parents) still reside here. I keep in touch with a couple of close friends who still live here and meet up for coffee from time to time. But outside of that, its as though everyone had died and you never see them again. Even though we all use the same supermarket, retail stores, public library, public transportation, and attend town events like a parade or a marathon.

I know some of you will reply "you got social media like Facebook or Instagram so you can see and catch up with them that way"... Well, I understand that, and I use Facebook where I keep in touch with lots of them online. But I am only talking about encountering them face-to-face which is very different.