Iterated in-person interactions fundamentally build trust.
If someone screws us over and we never see them again, it's hard to punish them.
But if we see them again we can make them feel ashamed, especially in front of other people.
If you don't see them in person, it's much easier for them to escape into the night.
If you never see them again, they can do bad faith things and not feel as bad.
Unlocked doors allow some honest people to fall into being dishonest.
If you see the same person again and again in person, you can trust them, because if they acted poorly, you'd likely see them again and be able to make them feel ashamed.
This is one of the reasons people react so strongly in road rage; they intuit they won't see the person again, so might as well make them feel maximally ashamed and scared right now.
A heuristic built into our firmware that mostly works, but in the modern world leads to some less than ideal outcomes.