This is an incredibly important point - you could remove the car entirely, even make you dependent on others (as you're dependent - or were before self checkout - on the Costco clerk) - and you still would have the disconnect.

Hardship can force it more often, perhaps, but that is accidental and secondary.

In all the times I've traveled on forms of "mass transit" (airplanes, subways, trains) the only time I've ever really talked to someone was at the seat-together dining on a long-distance train. Otherwise you can sit next to someone for 20+ hours and never say much more than "excuse me" if you need to use the restroom.

(Another counter to this is kids, if you have kids and there are kids anywhere within screaming distance, they will find each other and immediately be best friends. Parents get dragged along - https://www.bluey.tv/watch/season-2/cafe/ )