It's basically the difference between a village and a city. Reddit used to be like a bunch of villages, now it's like apartment buildings in the same city. Everyone is always a stranger in a city, people are always coming and going. You can walk down the same street the same time every day and see new faces every time.
That is exactly the same dynamic as is present on most of Reddit. Almost everyone you see is a stranger. Used to be (especially on old forums) you had some sort of relationship to the people you interacted with, you had a feel for their personality. Now it's just yet-another-new-username.
I think this is a major part of why there is so much tribalism online lately. People are desperately latching onto any sense of common identity to have something in common with the strangers they keep meeting.
