I see your point, but I think it's broader than something that can be attributed solely to cars.
I've lived in apartments and condos in the hearts of major American cities my entire adult life, and I'm surrounded by the same phenomenon in different form. I know maybe 3 of my neighbors in the hall from walking past them and saying hi once in a while, but besides that, I have basically no contact with them.
My partner grew up in an eastern European country and she tells stories of how, on holidays, people would go out to the hallways of her apartment building to congregate and drink and hang out. This concept seems totally alien to me. I'm pretty sure if a resident tried congregating in the hallways of any of the buildings I've lived in, security would be called to clear them out.
I've only lived in urban well-off-millennial type places. Maybe this is something unique to the upper-middle class and above. But I don't think it's entirely about suburbia.